[Federal Register Volume 75, Number 26 (Tuesday, February 9, 2010)]
[Rules and Regulations]
[Pages 6474-6537]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2010-1990]
[[Page 6473]]
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Part III
Environmental Protection Agency
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40 CFR Parts 50 and 58
Primary National Ambient Air Quality Standards for Nitrogen Dioxide;
Final Rule
Federal Register / Vol. 75, No. 26 / Tuesday, February 9, 2010 /
Rules and Regulations
[[Page 6474]]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 50 and 58
[EPA-HQ-OAR-2006-0922; FRL 9107-9]
RIN 2060-AO19
Primary National Ambient Air Quality Standards for Nitrogen
Dioxide
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
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SUMMARY: Based on its review of the air quality criteria for oxides of
nitrogen and the primary national ambient air quality standard (NAAQS)
for oxides of nitrogen as measured by nitrogen dioxide
(NO2), EPA is making revisions to the primary NO2
NAAQS in order to provide requisite protection of public health.
Specifically, EPA is establishing a new 1-hour standard at a level of
100 ppb, based on the 3-year average of the 98th percentile of the
yearly distribution of 1-hour daily maximum concentrations, to
supplement the existing annual standard. EPA is also establishing
requirements for an NO2 monitoring network that will include
monitors at locations where maximum NO2 concentrations are
expected to occur, including within 50 meters of major roadways, as
well as monitors sited to measure the area-wide NO2
concentrations that occur more broadly across communities.
DATES: This final rule is effective on April 12, 2010.
ADDRESSES: EPA has established a docket for this action under Docket ID
No. EPA-HQ-OAR-2006-0922. All documents in the docket are listed on the
http://www.regulations.gov Web site. Although listed in the index, some
information is not publicly available, e.g., confidential business
information or other information whose disclosure is restricted by
statute. Certain other material, such as copyrighted material, will be
publicly available only in hard copy form. Publicly available docket
materials are available either electronically through http://www.regulations.gov or in hard copy at the Air and Radiation Docket and
Information Center, EPA/DC, EPA West, Room 3334, 1301 Constitution
Ave., NW., Washington, DC. The Public Reading Room is open from 8:30
a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The
telephone number for the Public Reading Room is (202) 566-1744 and the
telephone number for the Air and Radiation Docket and Information
Center is (202) 566-1742.
FOR FURTHER INFORMATION CONTACT: Dr. Scott Jenkins, Health and
Environmental Impacts Division, Office of Air Quality Planning and
Standards, U.S. Environmental Protection Agency, Mail code C504-06,
Research Triangle Park, NC 27711; telephone: 919-541-1167; fax: 919-
541-0237; e-mail: [email protected].
SUPPLEMENTARY INFORMATION:
Table of Contents
The following topics are discussed in this preamble:
I. Background
A. Summary of Revisions to the NO2 Primary NAAQS
B. Legislative Requirements
C. Related NO2 Control Programs
D. Review of the Air Quality Criteria and Standards for Oxides
of Nitrogen
E. Summary of Proposed Revisions to the NO2 Primary
NAAQS
F. Organization and Approach to Final NO2 Primary
NAAQS Decisions
II. Rationale for Final Decisions on the NO2 Primary
Standard
A. Characterization of NO2 Air Quality
1. Current Patterns of NO2 Air Quality
2. NO2 Air Quality and Gradients Around Roadways
B. Health Effects Information
1. Adverse Respiratory Effects and Short-Term Exposure to
NO2
2. Other Effects With Short-Term Exposure to NO2
a. Mortality
b. Cardiovascular Effects
3. Health Effects With Long-Term Exposure to NO2
a. Respiratory Morbidity
b. Mortality
c. Carcinogenic, Cardiovascular, and Reproductive/Developmental
Effects
4. NO2-Related Impacts on Public Health
C. Human Exposure and Health Risk Characterization
D. Approach for Reviewing the Need To Retain or Revise the
Current Standard
E. Adequacy of the Current Standard
1. Rationale for Proposed Decision
2. Comments on the Adequacy of the Current Standard
a. Comments on EPA's Interpretation of the Epidemiologic
Evidence
b. Comments on EPA's Interpretation of the Controlled Human
Exposure Evidence
c. Comments on EPA's Characterization of NO2-
Associated Exposures and Health Risks
3. Conclusions on the Adequacy of the Current Standard
F. Elements of a New Short-Term Standard
1. Indicator
a. Rationale for Proposed Decision
b. Comments on Indicator
c. Conclusions Regarding Indicator
2. Averaging Time
a. Rationale for Proposed Decision
b. Comments on Averaging Time
c. Conclusions on Averaging Time
3. Form
a. Rationale for Proposed Decision
b. CASAC and Public Comments on Form
c. Conclusions on Form
4. Level
a. Rationale for Proposed Decisions on Approach and Level
b. Rationale for Alternative Decisions on Approach and Level
c. Comments on Approach and Level
i. CASAC Comments on the Approach to Setting the Standard
ii. Public Comments on the Approach To Setting the Standard
iii. CASAC Comments on Standard Level
iv. Public Comments on Standard Level
d. Conclusions on Approach and Standard Level
G. Annual Standard
H. Summary of Final Decisions on the Primary NO2
Standard
III. Amendments to Ambient Monitoring and Reporting Requirements
A. Monitoring Methods
1. Chemiluminescence FRM and Alternative Methods
2. Allowable FRM and FEMs for Comparison to the NAAQS
a. Proposed Changes to FRM and FEMs That May Be Compared to the
NAAQS
b. Comments
c. Decisions on Allowable FRM and FEMs for Comparison to the
NAAQS
B. Network Design
1. Two-Tiered Network Design
a. Proposed Two-Tier Network Design
b. Comments
c. Conclusions Regarding the Two-Tier Network Design
2. First Tier (Near-road Monitoring Component) of the
NO2 Network Design
a. Proposed First Tier (Near-road Monitoring Component) of the
Network Design
b. Comments
c. Conclusions Regarding the First Tier (Near-road Monitoring
Component) of the Network Design
3. Second Tier (Area-wide Monitoring Component) of the Network
Design
a. Proposed Second Tier (Area-wide Monitoring Component) of the
Network Design
b. Comments
c. Conclusions on the Second Tier (Area-wide Monitoring
Component) of the Network Design
4. Regional Administrator Authority
a. Proposed Regional Administrator Authority
b. Comments
c. Conclusions on Regional Administrator Authority
5. Monitoring Network Implementation
a. Proposed Monitoring Network Implementation Approach
b. Comments
c. Conclusions on Monitoring Network Implementation
6. Near-Road Site Selection
a. Proposed Near-Road Site Selection Criterion
b. Comments
c. Conclusions on Near-Road Site Selection
7. Near-Road Siting Criteria
a. Proposed Near-Road Siting Criteria
b. Comments
c. Conclusions on Near-Road Siting Criteria
8. Area-wide Monitor Site Selection and Siting Criteria
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a. Proposed Area-wide Monitor Site Selection and Siting Criteria
b. Comments
c. Conclusions on Area-Wide Monitor Site Selection and Siting
Criteria
9. Meteorological Measurements
a. Proposed Meteorological Measurements
b. Comments
c. Conclusions on Meteorological Measurements
C. Data Reporting
1. Proposed Data Quality Objectives and Measurement Uncertainty
2. Comments
3. Conclusions on Data Quality Objectives and Measurement
Uncertainty
IV. Appendix S--Interpretation of the Primary NAAQS for Oxides of
Nitrogen and Revisions to the Exceptional Events Rule
A. Interpretation of the Primary NAAQS for Oxides of Nitrogen
for the Annual Primary Standard
1. Proposed Interpretation of the Annual Standard
2. Comments on Interpretation of the Annual Standard
3. Conclusions on Interpretation of the Annual Standard
B. Interpretation of the Primary NAAQS for Oxides of Nitrogen 1-
Hour Primary Standard
1. Proposed Interpretation of the 1-Hour Standard
2. Comments on Interpretation of the 1-Hour Standard
3. Conclusions on Interpretation of the 1-Hour Standard
C. Exceptional Events Information Submission Schedule
V. Designation of Areas
A. Proposed Process
B. Public Comments
C. Final Designations Process
VI. Clean Air Act Implementation Requirements
A. Classifications
1. Proposal
2. Public comments
3. Final
B. Attainment Dates
1. Attaining the NAAQS
a. Proposal
b. Final
2. Consequences of Failing to Attain by the Statutory Attainment
Date
a. Proposal
b. Final
C. Section 110(a)(2) NAAQS Infrastructure Requirements
1. Proposal
2. Final
D. Attainment Planning Requirements
1. Nonattainment Area SIPs
a. Proposal
b. Public Comments
c. Final
2. New Source Review and Prevention of Significant Deterioration
Requirements
a. Proposal
b. Public Comments
c. Final
3. General Conformity
a. Proposal
4. Transportation Conformity
a. Proposal
b. Public Comments
c. Final
VII. Communication of Public Health Information
VIII. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review
B. Paperwork Reduction Act
C. Regulatory Flexibility Act
D. Unfunded Mandates Reform Act
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
G. Executive Order 13045: Protection of Children From
Environmental Health & Safety Risks
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution or Use
I. National Technology Transfer and Advancement Act
J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations
K. Congressional Review Act
References
I. Background
A. Summary of Revisions to the NO2 Primary NAAQS
Based on its review of the air quality criteria for oxides of
nitrogen and the primary national ambient air quality standard (NAAQS)
for oxides of nitrogen as measured by nitrogen dioxide
(NO2), EPA is making revisions to the primary NO2
NAAQS in order to provide requisite protection of public health as
appropriate under section 109 of the Clean Air Act (Act or CAA).
Specifically, EPA is supplementing the existing annual standard for
NO2 of 53 parts per billion (ppb) by establishing a new
short-term standard based on the 3-year average of the 98th percentile
of the yearly distribution of 1-hour daily maximum concentrations. EPA
is setting the level of this new standard at 100 ppb. EPA is making
changes in data handling conventions for NO2 by adding
provisions for this new 1-hour primary standard. EPA is also
establishing requirements for an NO2 monitoring network.
These new provisions require monitors at locations where maximum
NO2 concentrations are expected to occur, including within
50 meters of major roadways, as well as monitors sited to measure the
area-wide NO2 concentrations that occur more broadly across
communities. EPA is making conforming changes to the air quality index
(AQI).
B. Legislative Requirements
Two sections of the CAA govern the establishment and revision of
the NAAQS. Section 108 of the Act directs the Administrator to identify
and list air pollutants that meet certain criteria, including that the
air pollutant ``in [her] judgment, cause[s] or contribute[s] to air
pollution which may reasonably be anticipated to endanger public health
and welfare'' and ``the presence of which in the ambient air results
from numerous or diverse mobile or stationary sources.'' 42 U.S.C. 21
7408(a)(1)(A) & (B). For those air pollutants listed, section 108
requires the Administrator to issue air quality criteria that
``accurately reflect the latest scientific knowledge useful in
indicating the kind and extent of all identifiable effects on public
health or welfare which may be expected from the presence of [a]
pollutant in ambient air * * *'' 42 U.S.C. 7408(2).
Section 109(a) of the Act directs the Administrator to promulgate
``primary'' and ``secondary'' NAAQS for pollutants for which air
quality criteria have been issued. 42 U.S.C. 7409(1).\1\ Section
109(b)(1) defines a primary standard as one ``the attainment and
maintenance of which in the judgment of the Administrator, based on
[the air quality] criteria and allowing an adequate margin of safety,
are requisite to protect the public health.'' \2\ 42 U.S.C. 7409(b)(1).
A secondary standard, in turn, must ``specify a level of air quality
the attainment and maintenance of which, in the judgment of the
Administrator, based on [the air quality] criteria, is requisite to
protect the public welfare from any known or anticipated adverse
effects associated with the presence of such pollutant in the ambient
air.'' \3\ 42 U.S.C. 7409(b)(2).
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\1\ EPA notes that as the promulgation of a NAAQS is identified
in section 307(d)(1) of the Clean Air Act, all of the provisions of
this rulemaking are subject to the requirements of section 307(d) of
the Clean Air Act.
\2\ The legislative history of section 109 indicates that a
primary standard is to be set at ``the maximum permissible ambient
air level * * * which will protect the health of any [sensitive]
group of the population,'' and that for this purpose ``reference
should be made to a representative sample of persons comprising the
sensitive group rather than to a single person in such a group.'' S.
Rep. No. 91-1196, 91st Cong., 2d Sess. 10(1970).
\3\ EPA is currently conducting a separate review of the
secondary NO2 NAAQS jointly with a review of the
secondary SO2 NAAQS.
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The requirement that primary standards include an adequate margin
of safety is intended to address uncertainties associated with
inconclusive scientific and technical information available at the time
of standard setting. It is also intended to provide a reasonable degree
of protection against hazards that research has not yet identified.
Lead Industries Association v. EPA, 647 F.2d 1130, 1154 (DC Cir 1980),
cert. denied, 449 U.S.
[[Page 6476]]
1042 (1980); American Petroleum Institute v. Costle, 665 F.2d 1176,
1186 (DC Cir. 1981), cert. denied, 455 U.S. 1034 (1982). Both kinds of
uncertainties are components of the risk associated with pollution at
levels below those at which human health effects can be said to occur
with reasonable scientific certainty. Thus, in selecting primary
standards that include an adequate margin of safety, the Administrator
is seeking not only to prevent pollution levels that have been
demonstrated to be harmful but also to prevent lower pollutant levels
that may pose an unacceptable risk of harm, even if the risk is not
precisely identified as to nature or degree.
In addressing the requirement for a margin of safety, EPA considers
such factors as the nature and severity of the health effects involved,
the size of the at-risk population(s), and the kind and degree of the
uncertainties that must be addressed. The selection of any particular
approach to providing an adequate margin of safety is a policy choice
left specifically to the Administrator's judgment. Lead Industries
Association v. EPA, supra, 647 F.2d at 1161-62.
In setting standards that are ``requisite'' to protect public
health and welfare, as provided in section 109(b), EPA's task is to
establish standards that are neither more nor less stringent than
necessary for these purposes. In so doing, EPA may not consider the
costs of implementing the standards. Whitman v. American Trucking
Associations, 531 U.S. 457, 471, 475-76 (2001).
Section 109(d)(1) of the Act requires the Administrator to
periodically undertake a thorough review of the air quality criteria
published under section 108 and the NAAQS and to revise the criteria
and standards as may be appropriate. 42 U.S.C. 7409(d)(1). The Act also
requires the Administrator to appoint an independent scientific review
committee composed of seven members, including at least one member of
the National Academy of Sciences, one physician, and one person
representing State air pollution control agencies, to review the air
quality criteria and NAAQS and to ``recommend to the Administrator any
new * * * standards and revisions of existing criteria and standards as
may be appropriate under section 108 and subsection (b) of this
section.'' 42 U.S.C. 7409(d)(2). This independent review function is
performed by the Clean Air Scientific Advisory Committee (CASAC) of
EPA's Science Advisory Board.
C. Related NO2 Control Programs
States are primarily responsible for ensuring attainment and
maintenance of ambient air quality standards once EPA has established
them. Under section 110 of the Act, 42 U.S.C. 7410, and related
provisions, States are to submit, for EPA approval, State
implementation plans (SIPs) that provide for the attainment and
maintenance of such standards through control programs directed to
sources of the pollutants involved. The States, in conjunction with
EPA, also administer the prevention of significant deterioration
program that covers these pollutants. See 42 U.S.C. 7470-7479. In
addition, Federal programs provide for nationwide reductions in
emissions of these and other air pollutants under Title II of the Act,
42 U.S.C. 7521-7574, which involves controls for automobile, truck,
bus, motorcycle, nonroad engine and equipment, and aircraft emissions;
the new source performance standards under section 111 of the Act, 42
U.S.C. 7411; and the national emission standards for hazardous air
pollutants under section 112 of the Act, 42 U.S.C. 7412.
Currently there are no areas in the United States that are
designated as nonattainment of the NO2 NAAQS. With the
revisions to the NO2 NAAQS that result from this review,
however, some areas could be classified as non-attainment. Certain
States will be required to develop SIPs that identify and implement
specific air pollution control measures to reduce ambient
NO2 concentrations to attain and maintain the revised
NO2 NAAQS, most likely by requiring air pollution controls
on sources that emit oxides of nitrogen (NOX).\4\
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\4\ In this document, the terms ``oxides of nitrogen'' and
``nitrogen oxides'' (NOX) refer to all forms of oxidized
nitrogen (N) compounds, including NO, NO2, and all other
oxidized N-containing compounds formed from NO and NO2.
This follows usage in the Clean Air Act Section 108(c): ``Such
criteria [for oxides of nitrogen] shall include a discussion of
nitric and nitrous acids, nitrites, nitrates, nitrosamines, and
other carcinogenic and potentially carcinogenic derivatives of
oxides of nitrogen.'' By contrast, within the air pollution research
and control communities, the terms ``oxides of nitrogen'' and
``nitrogen oxides'' are restricted to refer only to the sum of NO
and NO2, and this sum is commonly abbreviated as
NOX. The category label used by this community for the
sum of all forms of oxidized nitrogen compounds including those
listed in Section 108(c) is NOY.
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While NOX is emitted from a wide variety of source
types, the top three categories of sources of NOX emissions
are on-road mobile sources, electricity generating units, and non-road
mobile sources. EPA anticipates that NOX emissions will
decrease substantially over the next 20 years as a result of the
ongoing implementation of mobile source emissions standards. In
particular, Tier 2 NOX emission standards for light-duty
vehicle emissions began phasing into the fleet beginning with model
year 2004, in combination with low-sulfur gasoline fuel standards. For
heavy-duty engines, new NOX standards are phasing in between
the 2007 and 2010 model years, following the introduction of ultra-low
sulfur diesel fuel. Lower NOX standards for nonroad diesel
engines, locomotives, and certain marine engines are becoming effective
throughout the next decade. In future decades, these lower-
NOX vehicles and engines will become an increasingly large
fraction of in-use mobile sources, effecting large NOX
emission reductions.
D. Review of the Air Quality Criteria and Standards for Oxides of
Nitrogen
On April 30, 1971, EPA promulgated identical primary and secondary
NAAQS for NO2 under section 109 of the Act. The standards
were set at 0.053 parts per million (ppm) (53 ppb), annual average (36
FR 8186). EPA completed reviews of the air quality criteria and
NO2 standards in 1985 and 1996 with decisions to retain the
standard (50 FR 25532, June 19, 1985; 61 FR 52852, October 8, 1996).
EPA initiated the current review of the air quality criteria for
oxides of nitrogen and the NO2 primary NAAQS on December 9,
2005 (70 FR 73236) with a general call for information. EPA's draft
Integrated Review Plan for the Primary National Ambient Air Quality
Standard for Nitrogen Dioxide (EPA, 2007a) was made available in
February, 2007 for public comment and was discussed by the CASAC via a
publicly accessible teleconference on May 11, 2007. As noted in that
plan, NOX includes multiple gaseous (e.g., NO2,
NO) and particulate (e.g., nitrate) species. Because the health effects
associated with particulate species of NOX have been
considered within the context of the health effects of ambient
particles in the Agency's review of the NAAQS for particulate matter
(PM), the current review of the primary NO2 NAAQS is focused
on the gaseous species of NOX and is not intended to address
health effects directly associated with particulate species.
The first draft of the Integrated Science Assessment for Oxides of
Nitrogen-Health Criteria (ISA) and the Nitrogen Dioxide Health
Assessment Plan: Scope and Methods for Exposure and Risk Assessment
(EPA, 2007b) were reviewed by CASAC at a public meeting held on October
24-25, 2007. Based on comments received from CASAC and the public, EPA
developed the second
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draft of the ISA and the first draft of the Risk and Exposure
Assessment to Support the Review of the NO2 Primary National
Ambient Air Quality Standard (Risk and Exposure Assessment (REA)).
These documents were reviewed by CASAC at a public meeting held on May
1-2, 2008. Based on comments received from CASAC and the public at this
meeting, EPA released the final ISA in July of 2008 (EPA, 2008a). In
addition, comments received were considered in developing the second
draft of the REA, which was released for public review and comment in
two parts. The first part of this document, containing chapters 1-7, 9
and appendices A and C as well as part of appendix B, was released in
August 2008. The second part of this document, containing chapter 8
(describing the Atlanta exposure assessment) and a completed appendix
B, was released in October of 2008. This document was the subject of
CASAC reviews at public meetings on September 9 and 10, 2008 (for the
first part) and on October 22, 2008 (for the second part). In preparing
the final REA (EPA, 2008b), EPA considered comments received from the
CASAC and the public at those meetings.
In the course of reviewing the second draft REA, CASAC expressed
the view that the document would be incomplete without the addition of
a policy assessment chapter presenting an integration of evidence-based
considerations and risk and exposure assessment results. CASAC stated
that such a chapter would be ``critical for considering options for the
NAAQS for NO2'' (Samet, 2008a). In addition, within the
period of CASAC's review of the second draft REA, EPA's Deputy
Administrator indicated in a letter to the chair of CASAC, addressing
earlier CASAC comments on the NAAQS review process, that the risk and
exposure assessment will include ``a broader discussion of the science
and how uncertainties may effect decisions on the standard'' and ``all
analyses and approaches for considering the level of the standard under
review, including risk assessment and weight of evidence
methodologies'' (Peacock, 2008, p. 3; September 8, 2008).
Accordingly, the final REA included a new policy assessment
chapter. This policy assessment chapter considered the scientific
evidence in the ISA and the exposure and risk characterization results
presented in other chapters of the REA as they relate to the adequacy
of the current NO2 primary NAAQS and potential alternative
primary NO2 standards. In considering the current and
potential alternative standards, the policy assessment chapter of the
final REA focused on the information that is most pertinent to
evaluating the basic elements of national ambient air quality
standards: Indicator, averaging time, form,\5\ and level. These
elements, which together serve to define each standard, must be
considered collectively in evaluating the health protection afforded.
CASAC discussed the final version of the REA, with an emphasis on the
policy assessment chapter, during a public teleconference held on
December 5, 2008. Following that teleconference, CASAC offered comments
and advice on the NO2 primary NAAQS in a letter to the
Administrator (Samet, 2008b).
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\5\ The ``form'' of a standard defines the air quality statistic
that is to be compared to the level of the standard in determining
whether an area attains the standard.
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The schedule for completion of this review is governed by a
judicial order resolving a lawsuit filed in September 2005, concerning
the timing of the current review. The order that now governs this
review, entered by the court in August 2007 and amended in December
2008, provides that the Administrator will sign, for publication,
notices of proposed and final rulemaking concerning the review of the
primary NO2 NAAQS no later than June 26, 2009 and January
22, 2010, respectively. In accordance with this schedule, the
Administrator signed a notice of proposed rulemaking on June 26, 2009
(FR 74 34404). This action presents the Administrator's final decisions
on the primary NO2 standard.
E. Summary of Proposed Revisions to the NO2 Primary NAAQS
For the reasons discussed in the preamble of the proposal for the
NO2 primary NAAQS (74 FR 34404), EPA proposed to make
revisions to the primary NO2 NAAQS and to make related
revisions for NO2 data handling conventions in order to
provide requisite protection of public health. EPA also proposed to
make corresponding changes to the AQI for NO2. Specifically,
EPA proposed to supplement the current annual standard by establishing
a new short-term NO2 standard that would reflect the maximum
allowable NO2 concentration anywhere in an area. EPA
proposed that this new short-term standard would be based on the 3-year
average of the 99th percentile (or 4th highest) of the yearly
distribution of 1[dash]hour daily maximum NO2 concentrations
and solicited comment on using the 3-year average of the 98th
percentile (or 7th or 8th highest) of the yearly distribution of 1-hour
daily maximum NO2 concentrations. EPA proposed to set the
level of this new 1-hour standard within the range of 80 to 100 ppb and
solicited comment on standard levels as low as 65 ppb and as high as
150 ppb. EPA proposed to specify the level of the standard to the
nearest ppb. EPA also proposed to establish requirements for an
NO2 monitoring network at locations where maximum
NO2 concentrations are expected to occur, including monitors
within 50 meters of major roadways, as well as area-wide monitors sited
to measure the NO2 concentrations that can occur more
broadly across communities. EPA also solicited comment on the
alternative approach of setting a 1-hour standard that would reflect
the allowable area-wide NO2 concentration.
F. Organization and Approach to Final NO2 Primary NAAQS Decisions
This action presents the Administrator's final decisions regarding
the need to revise the current NO2 primary NAAQS. Revisions
to the primary NAAQS for NO2, and the rationale supporting
those revisions, are described below in section II. Requirements for
the NO2 ambient monitoring network are described in section
III. Related requirements for data completeness, data handling, data
reporting, rounding conventions, and exceptional events are described
in section IV. Implementation of the revised NO2 primary
NAAQS is discussed in sections V and VI. Communication of public health
information through the AQI is discussed in section VII and a
discussion of statutory and executive order reviews is provided in
section VIII.
Today's final decisions are based on a thorough review in the ISA
of scientific information on known and potential human health effects
associated with exposure to NO2 in the air. These final
decisions also take into account: (1) Assessments in the REA of the
most policy-relevant information in the ISA as well as quantitative
exposure and risk analyses based on that information; (2) CASAC Panel
advice and recommendations, as reflected in its letters to the
Administrator and its public discussions of the ISA, the REA, and the
notice of proposed rulemaking; (3) public comments received during the
development of ISA and REA; and (4) public comments received on the
proposed rulemaking.
Some commenters have referred to and discussed individual
scientific analyses on the health effects of NO2 that were
not included in the ISA (EPA, 2008a) (``new studies''). In considering
[[Page 6478]]
and responding to comments for which such ``new studies'' were cited in
support, EPA has provisionally considered the cited studies in the
context of the findings of the ISA.
As in prior NAAQS reviews, EPA is basing its decision in this
review on studies and related information included in the ISA and
staff's policy assessment, which have undergone CASAC and public
review. In this NO2 NAAQS review, staff's policy assessment
was presented in the form of a policy assessment chapter of the REA
(EPA, 2008b). The studies assessed in the ISA and REA, and the
integration of the scientific evidence presented in them, have
undergone extensive critical review by EPA, CASAC, and the public. The
rigor of that review makes these studies, and their integrative
assessment, the most reliable source of scientific information on which
to base decisions on the NAAQS, decisions that all parties recognize as
of great import. NAAQS decisions can have profound impacts on public
health and welfare, and NAAQS decisions should be based on studies that
have been rigorously assessed in an integrative manner not only by EPA
but also by the statutorily mandated independent advisory committee, as
well as the public review that accompanies this process. EPA's
provisional consideration of ``new studies'' did not and could not
provide that kind of in-depth critical review.
This decision is consistent with EPA's practice in prior NAAQS
reviews and its interpretation of the requirements of the CAA. Since
the 1970 amendments, the EPA has taken the view that NAAQS decisions
are to be based on scientific studies and related information that have
been assessed as a part of the pertinent air quality criteria, and has
consistently followed this approach. This longstanding interpretation
was strengthened by new legislative requirements enacted in 1977, which
added section 109(d)(2) of the Act concerning CASAC review of air
quality criteria. See 71 FR 61144, 61148 (October 17, 2006) (final
decision on review of PM NAAQS) for a detailed discussion of this issue
and EPA's past practice.
As discussed in EPA's 1993 decision not to revise the NAAQS for
ozone (O3), ``new studies'' may sometimes be of such
significance that it is appropriate to delay a decision on revision of
a NAAQS and to supplement the pertinent air quality criteria so the
studies can be taken into account (58 FR at 13013-13014, March 9,
1993). In the present case, EPA's provisional consideration of ``new
studies'' concludes that, taken in context, the ``new'' information and
findings do not materially change any of the broad scientific
conclusions regarding the health effects of NO2 made in the
air quality criteria. For this reason, reopening the air quality
criteria review would not be warranted even if there were time to do so
under the court order governing the schedule for this rulemaking.
Accordingly, EPA is basing the final decisions in this review on
the studies and related information included in the NO2 air
quality criteria that have undergone CASAC and public review. EPA will
consider the ``new studies'' for purposes of decision-making in the
next periodic review of the NO2 NAAQS, which will provide
the opportunity to fully assess these studies through a more rigorous
review process involving EPA, CASAC, and the public. Further discussion
of these ``new studies'' can be found below, in section II.E, and in
the Response to Comments document.
II. Rationale for Final Decisions on the NO2 Primary
Standard
This section presents the rationale for the Administrator's
decision to revise the existing NO2 primary standard by
supplementing the current annual standard with a new 1-hour standard.
In developing this rationale, EPA has drawn upon an integrative
synthesis of the entire body of evidence on human health effects
associated with the presence of NO2 in the air. As
summarized below in section II.B, this body of evidence addresses a
broad range of health endpoints associated with exposure to
NO2. In considering this entire body of evidence, EPA
focuses in particular on those health endpoints for which the ISA finds
associations with NO2 to be causal or likely causal. This
rationale also draws upon the results of quantitative exposure and risk
assessments, summarized below in section II.C.
As discussed below, a substantial amount of new research has been
conducted since the last review of the NO2 NAAQS, with
important new information coming from epidemiologic studies in
particular. The newly available research studies evaluated in the ISA
have undergone intensive scrutiny through multiple layers of peer
review and opportunities for public review and comment. While important
uncertainties remain in the qualitative and quantitative
characterizations of health effects attributable to exposure to ambient
NO2, the review of this information has been extensive and
deliberate.
The remainder of this section provides background information that
informed the Administrator's decisions on the primary standard and
discusses the rationale for those decisions. Section II.A presents a
discussion of NO2 air quality. Section II.B includes an
overview of the scientific evidence related to health effects
associated with NO2 exposure. This overview includes
discussion of the health endpoints and at-risk populations considered
in the ISA. Section II.C discusses the approaches taken by EPA to
assess exposures and health risks associated with NO2,
including a discussion of key results. Section II.D summarizes the
approach that was used in the current review of the NO2
NAAQS with regard to consideration of the scientific evidence and
exposure-/risk-based results related to the adequacy of the current
standard and potential alternative standards. Sections II.E-II.G
discuss the Administrator's decisions regarding the adequacy of the
current standard, elements of a new 1-hour standard, and retention of
the current annual standard, respectively, taking into consideration
public comments on the proposed decisions. Section II.H summarizes the
Administrator's decisions with regard to the NO2 primary
NAAQS.
A. Characterization of NO2 Air Quality
1. Current Patterns of NO2 Air Quality
The size of the State and local NO2 monitoring network
has remained relatively stable since the early 1980s, and currently has
approximately 400 monitors reporting data to EPA's Air Quality System
(AQS) database.\6\ At present, there are no minimum monitoring
requirements for NO2 in 40 CFR part 58 Appendix D, other
than a requirement for EPA Regional Administrator approval before
removing any existing monitors, and that any ongoing NO2
monitoring must have at least one monitor sited to measure the maximum
concentration of NO2 in that area (though, as discussed
below monitors in the current network do not measure peak
concentrations associated with on-road mobile sources that can occur
near major roadways because the network was not designed for this
purpose). EPA removed the specific
[[Page 6479]]
minimum monitoring requirements for NO2 of two monitoring
sites per area with a population of 1,000,000 or more in the 2006
monitoring rule revisions (71 FR 61236), based on the fact that there
were no NO2 nonattainment areas at that time, coupled with
trends evidence showing an increasing gap between national average
NO2 concentrations and the current annual standard.
Additionally, the minimum requirements were removed to provide State,
local, and Tribal air monitoring agencies flexibility in meeting higher
priority monitoring needs for pollutants such as O3 and
PM2.5, or implementing the new multi-pollutant sites (NCore
network) required by the 2006 rule revisions, by allowing them to
discontinue lower priority monitoring. There are requirements in 40 CFR
part 58 Appendix D for NO2 monitoring as part of the
Photochemical Assessment Monitoring Stations (PAMS) network. However,
of the approximately 400 NO2 monitors currently in
operation, only about 10 percent may be due to the PAMS requirements.
---------------------------------------------------------------------------
\6\ It should be noted that the ISA (section 2.4.1) references a
different number of active monitors in the NO2 network.
The discrepancy between the ISA numbers and the number presented
here is due to differing metrics used in pulling data from AQS. The
ISA only references SLAMS, NAMS, and PAMS sites with defined
monitoring objectives, while Watkins and Thompson (2008) considered
all NO2 sites reporting data at any point during the
year. Based on this approach, Watkins and Thompson (2008) also noted
that the size of the NO2 monitoring network has remained
relatively stable since the early 1980s.
---------------------------------------------------------------------------
An analysis of the approximately 400 monitors comprising the
current NO2 monitoring network (Watkins and Thompson, 2008)
indicates that the current NO2 network has largely remained
unchanged in terms of size and target monitor objective categories
since it was introduced in the May 10, 1979 monitoring rule (44 FR
27571). The review of the current network found that the assessment of
concentrations for general population exposure and maximum
concentrations at neighborhood and larger scales were the top
objectives. A review of the distribution of listed spatial scales of
representation shows that only approximately 3 monitors are described
as microscale, representing an area on the order of several meters to
100 meters, and approximately 23 monitors are described as middle
scale, which represents an area on the order of 100 to 500 meters. This
low percentage of smaller spatially representative scale sites within
the network of approximately 400 monitoring sites indicates that the
majority of monitors have, in fact, been sited to assess area-wide
exposures on the neighborhood, urban, and regional scales, as would be
expected for a network sited to support the current annual
NO2 standard and PAMS objectives. The current network does
not include monitors placed near major roadways and, therefore,
monitors in the current network do not necessarily measure the maximum
concentrations that can occur on a localized scale near these roadways
(as discussed in the next section). It should be noted that the network
not only accommodates NAAQS related monitoring but also serves other
monitoring objectives, such as support for photochemistry analysis,
O3 modeling and forecasting, and particulate matter
precursor tracking.
2. NO2 Air Quality and Gradients Around Roadways
On-road and non-road mobile sources account for approximately 60%
of NOX emissions (ISA, table 2.2-1) and traffic-related
exposures can dominate personal exposures to NO2 (ISA
section 2.5.4). While driving, personal exposure concentrations in the
cabin of a vehicle could be substantially higher than ambient
concentrations measured nearby (ISA, section 2.5.4). For example,
estimates presented in the REA suggest that on/near roadway
NO2 concentrations could be approximately 80% (REA, section
7.3.2) higher on average across locations than concentrations away from
roadways and that roadway-associated environments could be responsible
for the majority of 1-hour peak NO2 exposures (REA, Figures
8-17 and 8-18). Because monitors in the current network are not sited
to measure peak roadway-associated NO2 concentrations,
individuals who spend time on and/or near major roadways could
experience NO2 concentrations that are considerably higher
than indicated by monitors in the current area-wide NO2
monitoring network.
Research suggests that the concentrations of on-road mobile source
pollutants such as NOX, carbon monoxide (CO), directly
emitted air toxics, and certain size distributions of particulate
matter (PM), such as ultrafine PM, typically display peak
concentrations on or immediately adjacent to roads (ISA, section 2.5).
This situation typically produces a gradient in pollutant
concentrations, with concentrations decreasing with increasing distance
from the road, and concentrations generally decreasing to near area-
wide ambient levels, or typical upwind urban background levels, within
a few hundred meters downwind. While such a concentration gradient is
present on almost all roads, the characteristics of the gradient,
including the distance from the road that a mobile source pollutant
signature can be differentiated from background concentrations, are
heavily dependent on factors such as traffic volumes, local topography,
roadside features, meteorology, and photochemical reactivity conditions
(Baldauf, et al., 2009; Beckerman et al., 2008; Clements et al., 2008;
Hagler et al., 2009; Janssen et al., 2001; Rodes and Holland, 1981;
Roorda-Knape et al., 1998; Singer et al., 2004; Zhou and Levy, 2007).
Because NO2 in the ambient air is due largely to the
atmospheric oxidation of NO emitted from combustion sources (ISA,
section 2.2.1), elevated NO2 concentrations can extend
farther away from roadways than the primary pollutants also emitted by
on-road mobile sources. More specifically, review of the technical
literature suggests that NO2 concentrations may return to
area-wide or typical urban background concentrations within distances
up to 500 meters of roads, though the actual distance will vary with
topography, roadside features, meteorology, and photochemical
reactivity conditions (Baldauf et al., 2009; Beckerman et al., 2008;
Clements et al., 2008; Gilbert et al. 2003; Rodes and Holland, 1981;
Singer et al., 2004; Zhou and Levy, 2007). Efforts to quantify the
extent and slope of the concentration gradient that may exist from peak
near-road concentrations to the typical urban background concentrations
must consider the variability that exists across locations and for a
given location over time. As a result, we have identified a range of
concentration gradients in the technical literature which indicate
that, on average, peak NO2 concentrations on or immediately
adjacent to roads may typically be between 30 and 100 percent greater
than concentrations monitored in the same area but farther away from
the road (ISA, Section 2.5.4; Beckerman et al., 2008; Gilbert et al.,
2003; Rodes and Holland, 1981; Roorda-Knape et al., 1998; Singer et
al., 2004). This range of concentration gradients has implications for
revising the NO2 primary standard and for the NO2
monitoring network (discussed in sections II.F.4 and III).
B. Health Effects Information
In the last review of the NO2 NAAQS, the 1993
NOX Air Quality Criteria Document (1993 AQCD) (EPA, 1993)
concluded that there were two key health effects of greatest concern at
ambient or near-ambient concentrations of NO2 (ISA, section
5.3.1). The first was increased airway responsiveness in asthmatic
individuals after short-term exposures. The second was increased
respiratory illness among children associated with longer-term
exposures to NO2. Evidence also was found for increased risk
of emphysema, but this appeared to be of major concern only with
exposures to NO2 at levels much higher than then current
ambient levels (ISA, section 5.3.1). Controlled human
[[Page 6480]]
exposure and animal toxicological studies provided qualitative evidence
for airway hyperresponsiveness and lung function changes while
epidemiologic studies provided evidence for increased respiratory
symptoms with increased indoor NO2 exposures. Animal
toxicological findings of lung host defense system changes with
NO2 exposure provided a biologically-plausible basis for the
epidemiologic results. Subpopulations considered potentially more
susceptible to the effects of NO2 exposure included persons
with preexisting respiratory disease, children, and the elderly. The
epidemiologic evidence for respiratory health effects was limited, and
no studies had considered endpoints such as hospital admissions,
emergency department visits, or mortality (ISA, section 5.3.1).
As summarized below and discussed more fully in section II.B of the
proposal notice, evidence published since the last review generally has
confirmed and extended the conclusions articulated in the 1993 AQCD
(ISA, section 5.3.2). The epidemiologic evidence has grown
substantially with the addition of field and panel studies,
intervention studies, time-series studies of endpoints such as hospital
admissions, and a substantial number of studies evaluating mortality
risk associated with short-term NO2 exposures. While not as
marked as the growth in the epidemiologic literature, a number of
recent toxicological and controlled human exposure studies also provide
insights into relationships between NO2 exposure and health
effects. This body of evidence focuses the current review on
NO2-related respiratory effects at lower ambient and
exposure concentrations than considered in the previous review.
1. Adverse Respiratory Effects and Short-Term Exposure to
NO2
The ISA concluded that the findings of epidemiologic, controlled
human exposure, and animal toxicological studies provide evidence that
is sufficient to infer a likely causal relationship for respiratory
effects following short-term NO2 exposure (ISA, sections
3.1.7 and 5.3.2.1). The ISA (section 5.4) concluded that the strongest
evidence for an association between NO2 exposure and adverse
human health effects comes from epidemiologic studies of respiratory
symptoms, emergency department visits, and hospital admissions. These
studies include panel and field studies, studies that control for the
effects of co-occurring pollutants, and studies conducted in areas
where the whole distribution of ambient 24-hour average NO2
concentrations was below the current NAAQS level of 53 ppb (annual
average). With regard to this evidence, the ISA concluded that
NO2 epidemiologic studies provide ``little evidence of any
effect threshold'' (ISA, section 5.3.2.9, p. 5-15). In studies that
have evaluated concentration-response relationships, they appear linear
within the observed range of data (ISA, section 5.3.2.9).
Overall, the epidemiologic evidence for respiratory effects has
been characterized in the ISA as consistent, in that associations are
reported in studies conducted in numerous locations with a variety of
methodological approaches, and coherent, in that the studies report
associations with respiratory health outcomes that are logically linked
together. In addition, a number of these associations are statistically
significant, particularly the more precise effect estimates (ISA,
section 5.3.2.1). These epidemiologic studies are supported by evidence
from toxicological and controlled human exposure studies, particularly
those that evaluated airway hyperresponsiveness in asthmatic
individuals (ISA, section 5.4). The ISA concluded that together, the
epidemiologic and experimental data sets form a plausible, consistent,
and coherent description of a relationship between NO2
exposures and an array of adverse respiratory health effects that range
from the onset of respiratory symptoms to hospital admissions.
In considering the uncertainties associated with the epidemiologic
evidence, the ISA (section 5.4) noted that it is difficult to determine
``the extent to which NO2 is independently associated with
respiratory effects or if NO2 is a marker for the effects of
another traffic-related pollutant or mix of pollutants.'' On-road
vehicle exhaust emissions are a widespread source of combustion
pollutant mixtures that include NOX and are an important
contributor to NO2 levels in near-road locations. Although
the presence of other pollutants from vehicle exhaust emissions
complicates efforts to quantify specific NO2-related health
effects, a number of epidemiologic studies have evaluated associations
with NO2 in models that also include co-occurring pollutants
such as PM, O3, CO, and/or SO2. The evidence
summarized in the ISA indicates that NO2 associations
generally remain robust in these multi-pollutant models and supports a
direct effect of short-term NO2 exposure on respiratory
morbidity (see ISA Figures 3.1-7, 3.1-10, 3.1-11). The plausibility and
coherence of these effects are also supported by epidemiologic studies
of indoor NO2 as well as experimental (i.e., toxicological
and controlled human exposure) studies that have evaluated host defense
and immune system changes, airway inflammation, and airway
responsiveness (see subsequent sections of this proposal and the ISA,
section 5.3.2.1). The ISA (section 5.4) concluded that the robustness
of epidemiologic findings to adjustment for co-pollutants, coupled with
data from animal and human experimental studies, support a
determination that the relationship between NO2 and
respiratory morbidity is likely causal, while still recognizing the
relationship between NO2 and other traffic related
pollutants.
The epidemiologic and experimental studies encompass a number of
respiratory-related health endpoints, including emergency department
visits and hospitalizations, respiratory symptoms, airway
hyperresponsiveness, airway inflammation, and lung function. The
findings relevant to these endpoints, which provide the rationale to
support the judgment of a likely causal relationship, are described in
more detail in section II.B.1 of the proposal.
2. Other Effects With Short-Term Exposure to NO2
a. Mortality
The ISA concluded that the epidemiologic evidence is suggestive,
but not sufficient, to infer a causal relationship between short-term
exposure to NO2 and all-cause and cardiopulmonary-related
mortality (ISA, section 5.3.2.3). Results from several large United
States and European multicity studies and a meta-analysis study
indicate positive associations between ambient NO2
concentrations and the risk of all-cause (nonaccidental) mortality,
with effect estimates ranging from 0.5 to 3.6% excess risk in mortality
per standardized increment (20 ppb for 24-hour averaging time, 30 ppb
for 1-hour averaging time) (ISA, section 3.3.1, Figure 3.3-2, section
5.3.2.3). In general, the ISA concluded that NO2 effect
estimates were robust to adjustment for co-pollutants. Both
cardiovascular and respiratory mortality have been associated with
increased NO2 concentrations in epidemiologic studies (ISA,
Figure 3.3-3); however, similar associations were observed for other
pollutants, including PM and SO2. The range of risk
estimates for excess mortality is generally smaller than that for other
pollutants such as PM. In addition, while NO2 exposure,
alone or in conjunction with other pollutants,
[[Page 6481]]
may contribute to increased mortality, evaluation of the specificity of
this effect is difficult. Clinical studies showing hematologic effects
and animal toxicological studies showing biochemical, lung host
defense, permeability, and inflammation changes with short-term
exposures to NO2 provide limited evidence of plausible
pathways by which risks of mortality may be increased, but no coherent
picture is evident at this time (ISA, section 5.3.2.3).
b. Cardiovascular Effects
The ISA concluded that the available evidence on cardiovascular
health effects following short-term exposure to NO2 is
inadequate to infer the presence or absence of a causal relationship at
this time (ISA, section 5.3.2.2). Evidence from epidemiologic studies
of heart rate variability, repolarization changes, and cardiac rhythm
disorders among heart patients with ischemic cardiac disease are
inconsistent (ISA, section 5.3.2.2). In most studies, associations with
PM were found to be similar or stronger than associations with
NO2. Generally positive associations between ambient
NO2 concentrations and hospital admissions or emergency
department visits for cardiovascular disease have been reported in
single-pollutant models (ISA, section 5.3.2.2); however, most of these
effect estimate values were diminished in multi-pollutant models that
also contained CO and PM indices (ISA, section 5.3.2.2). Mechanistic
evidence of a role for NO2 in the development of
cardiovascular diseases from studies of biomarkers of inflammation,
cell adhesion, coagulation, and thrombosis is lacking (ISA, section
5.3.2.2). Furthermore, the effects of NO2 on various
hematological parameters in animals are inconsistent and, thus, provide
little biological plausibility for effects of NO2 on the
cardiovascular system (ISA, section 5.3.2.2).
3. Health Effects With Long-Term Exposure to NO2
a. Respiratory Morbidity
The ISA concluded that overall, the epidemiologic and experimental
evidence is suggestive, but not sufficient, to infer a causal
relationship between long-term NO2 exposure and respiratory
morbidity (ISA, section 5.3.2.4). The available database evaluating the
relationship between respiratory illness in children and long-term
exposures to NO2 has increased since the 1996 review of the
NO2 NAAQS (see section II.B.3 of the proposal for a more
detailed discussion). A number of epidemiologic studies have examined
the effects of long-term exposure to NO2 and reported
positive associations with decrements in lung function and partially
irreversible decrements in lung function growth (ISA, section 3.4.1,
Figures 3.4-1 and 3.4-2). While animal toxicological studies may
provide biological plausibility for the chronic effects of
NO2 that have been observed in epidemiologic studies (ISA,
sections 3.4.5 and 5.3.2.4), the high correlation among traffic-related
pollutants in epidemiologic studies makes it difficult to accurately
estimate independent effects (ISA, section 5.3.2.4).
b. Mortality
The ISA concluded that the epidemiologic evidence is inadequate to
infer the presence or absence of a causal relationship between long-
term exposure to NO2 and mortality (ISA, section 5.3.2.6).
In the United States and European cohort studies examining the
relationship between long-term exposure to NO2 and
mortality, results have been inconsistent (ISA, section 5.3.2.6).
Further, when associations were suggested, they were not specific to
NO2 but also implicated PM and other traffic indicators. The
relatively high correlations reported between NO2 and PM
indices make it difficult to interpret these observed associations at
this time (ISA, section 5.3.2.6).
c. Carcinogenic, cardiovascular, and reproductive/developmental effects
The ISA concluded that the available epidemiologic and
toxicological evidence is inadequate to infer the presence or absence
of a causal relationship for carcinogenic, cardiovascular, and
reproductive and developmental effects related to long-term
NO2 exposure (ISA, section 5.3.2.5). Epidemiologic studies
conducted in Europe have shown an association between long-term
NO2 exposure and increased incidence of cancer (ISA, section
5.3.2.5). However, the animal toxicological studies have provided no
clear evidence that NO2 acts as a carcinogen (ISA, section
5.3.2.5). The very limited epidemiologic and toxicological evidence do
not suggest that long-term exposure to NO2 has
cardiovascular effects (ISA, section 5.3.2.5). The epidemiologic
evidence is not consistent for associations between NO2
exposure and fetal growth retardation; however, some evidence is
accumulating for effects on preterm delivery (ISA, section 5.3.2.5).
Scant animal evidence supports a weak association between
NO2 exposure and adverse birth outcomes and provides little
mechanistic information or biological plausibility for the
epidemiologic findings.
4. NO2-related Impacts on Public Health
Specific groups within the general population are likely at
increased risk for suffering adverse effects from NO2
exposure. This could occur because they are affected by lower levels of
NO2 than the general population or because they experience a
larger health impact than the general population to a given level of
exposure (susceptibility) and/or because they are exposed to higher
levels of NO2 than the general population (vulnerability).
The term susceptibility generally encompasses innate (e.g., genetic or
developmental) and/or acquired (e.g., age or disease) factors that make
individuals more likely to experience effects with exposure to
pollutants. The severity of health effects experienced by a susceptible
subgroup may be much greater than that experienced by the population at
large. Factors that may influence susceptibility to the effects of air
pollution include age (e.g., infants, children, elderly); gender; race/
ethnicity; genetic factors; and pre-existing disease/condition (e.g.,
obesity, diabetes, respiratory disease, asthma, chronic obstructive
pulmonary disease (COPD), cardiovascular disease, airway
hyperresponsiveness, respiratory infection, adverse birth outcome)
(ISA, sections 4.3.1, 4.3.5, and 5.3.2.8). In addition, certain groups
may experience relatively high exposure to NO2, thus forming
a potentially vulnerable population (ISA, section 4.3.6). Factors that
may influence susceptibility and vulnerability to air pollution include
socioeconomic status (SES), education level, air conditioning use,
proximity to roadways, geographic location, level of physical activity,
and work environment (e.g., indoor versus outdoor) (ISA, section
4.3.5). The ISA discussed factors that can confer susceptibility and/or
vulnerability to air pollution with most of the discussion devoted to
factors for which NO2-specific evidence exists (ISA, section
4.3). These factors include pre-existing disease (e.g., asthma), age
(i.e., infants, children, older adults), genetic factors, gender,
socioeconomic status, and proximity to roadways (see section II.B.4 in
proposal for more detailed discussion of these factors).
As discussed in more detail in the proposal (section II.B.4), the
population potentially affected by NO2 is large. A
considerable fraction of the population resides, works, or attends
school near major roadways, and these individuals are likely to have
increased exposure to NO2 (ISA, section 4.4). Based on data
[[Page 6482]]
from the 2003 American Housing Survey, approximately 36 million
individuals live within 300 feet (~90 meters) of a four-lane highway,
railroad, or airport (ISA, section 4.4).\7\ Furthermore, in California,
2.3% of schools, with a total enrollment of more than 150,000 students
were located within approximately 500 feet of high-traffic roads, with
a higher proportion of non-white and economically disadvantaged
students attending those schools (ISA, section 4.4). Of this
population, asthmatics and members of other susceptible groups
discussed above will have even greater risks of experiencing health
effects related to NO2 exposure. In the United States,
approximately 10% of adults and 13% of children (approximately 22.2
million people in 2005) have been diagnosed with asthma, and 6% of
adults have been diagnosed with COPD (ISA, section 4.4). The prevalence
and severity of asthma is higher among certain ethnic or racial groups
such as Puerto Ricans, American Indians, Alaskan Natives, and African
Americans (ISA, section 4.4). A higher prevalence of asthma among
persons of lower SES and an excess burden of asthma hospitalizations
and mortality in minority and inner-city communities have been observed
(ISA, section 4.4). In addition, based on United States census data
from 2000, about 72.3 million (26%) of the United States population are
under 18 years of age, 18.3 million (7.4%) are under 5 years of age,
and 35 million (12%) are 65 years of age or older. Therefore, large
portions of the United States population are in age groups that are
likely at-risk for health effects associated with exposure to ambient
NO2. The size of the potentially at-risk population suggests
that exposure to ambient NO2 could have a significant impact
on public health in the United States.
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\7\ The most current American Housing Survey (http://www.census.gov/hhes/www/housing/ahs/ahs.html) is from 2007 and lists
a higher fraction of housing units within the 300 foot boundary than
do prior surveys. According to Table 1A-6 from that report (http://www.census.gov/hhes/www/housing/ahs/ahs07/tab1a-6.pdf), out of
128,203,000 total housing units in the United States, 20,016,000
were reported by the surveyed occupant or landlord as being within
300 feet of a 4-or-more lane highway, railroad, or airport. That
constitutes 15.613% of the total housing units in the U.S. Assuming
equal distributions, with a current population of 306,330,199, that
means that there would be 47.8 million people meeting the 300 foot
criteria.
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C. Human Exposure and Health Risk Characterization
To put judgments about NO2-associated health effects
into a broader public health context, EPA has drawn upon the results of
the quantitative exposure and risk assessments. Judgments reflecting
the nature of the evidence and the overall weight of the evidence are
taken into consideration in these quantitative exposure and risk
assessments, discussed below. These assessments provide estimates of
the likelihood that asthmatic individuals would experience exposures of
potential concern and estimates of the incidence of NO2-
associated respiratory emergency department visits under varying air
quality scenarios (e.g., just meeting the current or alternative
standards), as well as characterizations of the kind and degree of
uncertainties inherent in such estimates. As discussed more fully in
section II.C of the proposal, this section summarizes the approach
taken in the REA to characterize NO2-related exposures and
health risks. Goals of the REA included estimating short-term exposures
and potential human health risks associated with (1) recent levels of
ambient NO2; (2) NO2 levels adjusted to simulate
just meeting the current standard; and (3) NO2 levels
adjusted to simulate just meeting potential alternative standards.
For purposes of the quantitative characterization of NO2
health risks, the REA determined that it was appropriate to focus on
endpoints for which the ISA concluded that the available evidence is
sufficient to infer either a causal or a likely causal relationship.
This was generally consistent with judgments made in other recent NAAQS
reviews (e.g., see EPA, 2005). As noted above in section II.A, the only
health effect category for which the evidence was judged in the ISA to
be sufficient to infer either a causal or a likely causal relationship
is respiratory morbidity following short-term NO2 exposure.
Therefore, for purposes of characterizing health risks associated with
NO2, the REA focused on respiratory morbidity endpoints that
have been associated with short-term NO2 exposures.
In evaluating the appropriateness of specific endpoints for use in
the NO2 risk characterization, the REA considered both
epidemiologic and controlled human exposure studies. As described in
more detail in the proposal (section II.C.1), the characterization of
NO2-associated health risks was based on an epidemiology
study conducted in Atlanta, Georgia by Tolbert et al. (2007) and a
meta-analysis of controlled human exposure studies of NO2
and airway responsiveness in asthmatics (ISA, Table 3.1-3).\8\
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\8\ The study by Tolbert et al. (2007) reported positive
associations between 1-hour ambient NO2 concentrations
and respiratory-related emergency department visits. The meta-
analysis was included in the ISA and reported that short-term
exposures to NO2 concentrations at or above 100 ppb
increased airway responsiveness in most asthmatics.
---------------------------------------------------------------------------
As noted above, the purpose of the assessments described in the REA
was to characterize air quality, exposures, and health risks associated
with recent ambient levels of NO2, with NO2
levels that could be associated with just meeting the current
NO2 NAAQS, and with NO2 levels that could be
associated with just meeting potential alternative standards. To
characterize health risks, the REA employed three approaches. In the
first approach, for each air quality scenario, NO2
concentrations at fixed-site monitors and simulated concentrations on/
near roadways were compared to potential health effect benchmark values
derived from the controlled human exposure literature. In the second
approach, modeled estimates of exposures in asthmatics were compared to
potential health effect benchmarks. In the third approach,
concentration-response relationships from an epidemiologic study were
used in conjunction with baseline incidence data and recent or
simulated ambient concentrations to estimate health impacts. An
overview of the approaches to characterizing health risks is provided
in the proposal (section II.C.2) and each approach, along with its
limitations and uncertainties (see proposal, section II.C.3) has been
described in more detail in the REA (chapters 6 through 9).
Chapters 7-9 of the REA estimated exposures and health risks
associated with recent air quality and with air quality, as measured at
monitors in the current area-wide network, which had been adjusted to
simulate just meeting the current and potential alternative standards.
The specific standard levels evaluated, for an area-wide standard based
on the 3-year average of the 98th and 99th percentile 1-hour daily
maximum NO2 concentrations, were 50, 100, 150, and 200 ppb.
In interpreting these results within the context of the current
revisions to the NO2 primary NAAQS (see below), we note that
simulation of different standard levels was based on adjusting
NO2 concentrations at available area-wide monitors.
Therefore, the standard levels referred to above reflect the allowable
area-wide NO2 concentrations, not the maximum allowable
concentrations. As a consequence, the maximum concentrations in an area
that just meets one of these standard levels would be expected to be
higher than the standard level. For example, given that near-road
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NO2 concentrations can be 30% to 100% higher than area-wide
concentrations (see section II.E.2), an area-wide concentration of 50
ppb could correspond to near-road concentrations from 65 to 100 ppb.
Key results of the air quality, exposure, and risk analyses were
presented in the policy assessment chapter of the REA and summarized in
the proposal (Table 1 in proposal). In considering these results, the
policy assessment chapter of the REA concluded that the risks estimated
to be associated with just meeting the current annual standard can be
judged important from a public health perspective. The results for
specific 1-hour standard levels estimate that limiting the 98th/99th
percentile of the distribution of 1-hour daily maximum NO2
concentrations measured at area-wide monitors to 50 or 100 ppb could
substantially reduce exposures to ambient NO2 and associated
health risks (compared to just meeting the current standard). In
contrast, limiting these area-wide NO2 concentrations to 150
or 200 ppb is estimated to result in similar, or in some cases higher,
NO2-associated exposures and health risks than just meeting
the current standard. The pattern of results was similar for standards
just meeting either the 98th or the 99th percentile 1-hour daily
maximum area-wide standards (REA, Chapters 7, 8, and 9).
D. Approach for Reviewing the Need To Retain or Revise the Current
Standard
EPA notes that the final decision on retaining or revising the
current primary NO2 standard is a public health policy
judgment to be made by the Administrator. This judgment has been
informed by a recognition that the available health effects evidence
reflects a continuum consisting of ambient levels of NO2 at
which scientists generally agree that health effects are likely to
occur, through lower levels at which the likelihood and magnitude of
the response become increasingly uncertain. The Administrator's final
decisions draw upon scientific information and analyses related to
health effects, population exposures, and risks; judgments about the
appropriate response to the range of uncertainties that are inherent in
the scientific evidence and analyses; and comments received from CASAC
and the public.
To evaluate whether the current primary NO2 standard is
requisite or whether consideration of revisions is appropriate, EPA has
used an approach in this review that was described in the policy
assessment chapter of the REA. This approach builds upon those used in
reviews of other criteria pollutants, including the most recent reviews
of the Pb, O3, and PM NAAQS (EPA, 2007c; EPA, 2007d; EPA,
2005), and reflects the body of evidence and information that is
currently available. As in other recent reviews, EPA's considerations
included the implications of placing more or less weight or emphasis on
different aspects of the scientific evidence and the exposure/risk-
based information, recognizing that the weight to be given to various
elements of the evidence and exposure/risk information is part of the
public health policy judgments that the Administrator will make in
reaching decisions on the standard.
A series of general questions framed this approach to considering
the scientific evidence and exposure-/risk-based information. First,
EPA's consideration of the scientific evidence and exposure/risk
information with regard to the adequacy of the current standard has
been framed by the following questions:
To what extent does evidence that has become available
since the last review reinforce or call into question evidence for
NO2-associated effects that were identified in the last
review?
To what extent has evidence for different health
effects and/or sensitive populations become available since the last
review?
To what extent have uncertainties identified in the
last review been reduced and/or have new uncertainties emerged?
To what extent does evidence and exposure-/risk-based
information that has become available since the last review
reinforce or call into question any of the basic elements of the
current standard?
To the extent that the available evidence and exposure-/risk-based
information suggests it may be appropriate to consider revision of the
current standard, EPA considers that evidence and information with
regard to its support for consideration of a standard that is either
more or less protective than the current standard. This evaluation has
been framed by the following questions:
Is there evidence that associations, especially causal
or likely causal associations, extend to ambient NO2
concentrations as low as, or lower than, the concentrations that
have previously been associated with health effects? If so, what are
the important uncertainties associated with that evidence?
Are exposures above benchmark levels and/or health
risks estimated to occur in areas that meet the current standard? If
so, are the estimated exposures and health risks important from a
public health perspective? What are the important uncertainties
associated with the estimated risks?
To the extent that there is support for consideration of a revised
standard, EPA then considers the specific elements of the standard
(indicator, averaging time, form, and level) within the context of the
currently available information. In so doing, the Agency has addressed
the following questions:
Does the evidence provide support for considering a
different indicator for gaseous NOX?
Does the evidence provide support for considering
different averaging times?
What ranges of levels and forms of alternative
standards are supported by the evidence, and what are the associated
uncertainties and limitations?
To what extent do specific averaging times, levels, and
forms of alternative standards reduce the estimated exposures above
benchmark levels and risks attributable to NO2, and what
are the uncertainties associated with the estimated exposure and
risk reductions?
The questions outlined above have been addressed in the REA, the
proposal, and in this final rulemaking. The following sections present
the rationale for proposed decisions, discussion of public comments,
and the Administrator's conclusions on the adequacy of the current
standard and potential alternative standards in terms of indicator,
averaging time, form, and level.
E. Adequacy of the Current Standard
This section discusses considerations related to the decision as to
whether the current NO2 primary NAAQS is requisite to
protect public health with an adequate margin of safety. Specifically,
section II.E.1 provides an overview of the rationale supporting the
Administrator's conclusion in the proposal that the current standard
alone does not provide adequate public health protection; section
II.E.2 discusses comments received on the adequacy of the current
standard; and section II.E.3 discusses the Administrator's final
decision on whether the current NO2 primary NAAQS is
requisite to protect public health with an adequate margin of safety.
1. Rationale for Proposed Decision
In reaching a conclusion regarding the adequacy of the current
NO2 NAAQS in the proposal (section II.E.5), the
Administrator considered the scientific evidence assessed in the ISA
and the conclusions of the ISA, the exposure and risk information
presented in the REA and the conclusions of the policy assessment
chapter of the REA, and the views expressed by CASAC. These
considerations are discussed in detail in the proposal (II.E.) and are
summarized in this section. In the proposal, the
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Administrator noted the following in considering the adequacy of the
current standard:
The ISA concluded that the results of epidemiologic and
experimental studies form a plausible and coherent data set that
supports a relationship between NO2 exposures and
respiratory endpoints, including respiratory symptoms and respiratory-
related hospital admissions and emergency department visits, at ambient
concentrations that are present in areas that meet the current
NO2 NAAQS (ISA, section 5.4).
The policy assessment chapter of the REA concluded that
risks estimated to be associated with air quality adjusted upward to
simulate just meeting the current standard can reasonably be judged
important from a public health perspective (REA, section 10.3.3).
The policy assessment chapter of the REA concluded that
exposure- and risk-based results reinforce the scientific evidence in
supporting the conclusion that consideration should be given to
revising the current NO2 NAAQS so as to provide increased
public health protection, especially for at-risk groups, from
NO2-related adverse health effects associated with short-
term, and potential long-term, exposures (REA, section 10.3.3).
CASAC agreed that the current annual standard alone is not
sufficient to protect public health against the types of exposures that
could lead to these health effects. Specifically, in their letter to
the Administrator on the final REA, they stated that ``CASAC concurs
with EPA's judgment that the current NAAQS does not protect the
public's health and that it should be revised'' (Samet, 2008b).
Based on these considerations (discussed in more detail in the
proposal, section II.E), the Administrator concluded in the proposal
that the current NO2 primary NAAQS is not requisite to
protect public health with an adequate margin of safety against adverse
respiratory effects associated with short-term exposures. In
considering approaches to revising the current standard, the
Administrator concluded that it is appropriate to consider setting a
new short-term standard in addition to retaining the current annual
standard. The Administrator noted that such a short-term standard could
provide increased public health protection, especially for members of
at-risk groups, from effects described in both epidemiologic and
controlled human exposure studies to be associated with short-term
exposures to NO2.
2. Comments on the Adequacy of the Current Standard
This section discusses comments received from CASAC and public
commenters on the proposal that either supported or opposed the
Administrator's proposed decision to revise the current NO2
primary NAAQS. Comments on the adequacy of the current standard that
focused on the scientific and/or the exposure/risk basis for the
Administrator's proposed conclusions are discussed in sections
II.E.2.a-II.E.2.c. Comments on the epidemiologic evidence are
considered in section II.E.2.a. Comments on the controlled human
exposure evidence are considered in section II.E.2.b. Comments on human
exposure and health risk assessments are considered in section
II.E.2.c. To the extent these comments on the evidence and information
are also used to justify commenters' conclusions on decisions related
to indicator, averaging time, level, or form, they are noted in the
appropriate sections below (II.F.1-II.F.4).
In their comments on the proposal (Samet, 2009), CASAC reiterated
their support for the need to revise the current annual NO2
NAAQS in order to increase public health protection. As noted above, in
its letter to the Administrator on the final REA (Samet, 2008b) CASAC
stated that it ``concurs with EPA's judgment that the current NAAQS
does not protect the public's health and that it should be revised.''
In supporting adoption of a more stringent NAAQS for NO2,
CASAC considered the assessment of the scientific evidence presented in
the ISA, the results of assessments presented in the REA, and the
conclusions of the policy assessment chapter of the REA. As such,
CASAC's rationale for revising the current standard was consistent with
the Administrator's rationale as discussed in the proposal.
Many public commenters agreed with CASAC that, based on the
available information, the current NO2 standard is not
requisite to protect public health with an adequate margin of safety
and that revisions to the standard are appropriate. Among those calling
for revisions to the standard were environmental groups (e.g., Clean
Air Council (CAC), Earth Justice (EJ), Environmental Defense Fund
(EDF), Natural Resources Defense Council (NRDC), Group Against Smog and
Pollution (GASP)); medical/public health organizations (e.g., American
Lung Association (ALA), American Medical Association (AMA), American
Thoracic Society (ATS), National Association for the Medical Direction
of Respiratory Care (NAMDRC), National Association of Cardiovascular
and Pulmonary Rehabilitation (NACPR), American College of Chest
Physicians (ACCP)); a large number of State agencies and organizations
(e.g., National Association of Clean Air Agencies (NACAA), Northeast
States for Coordinated Air Use Management (NESCAUM), and State or local
agencies in CA, IA, IL, MI, MO, NC, NM, NY, TX, VA, WI); Tribes (e.g.,
National Tribal Air Association (NTAA), Fond du Lac Band of Lake
Superior Chippewa (Fond du Lac)), and a number of individual
commenters. These commenters concluded that the current NO2
standard needs to be revised and that a more stringent standard is
needed to protect the health of sensitive population groups. In
supporting the need to adopt a more stringent NAAQS for NO2,
these commenters often referenced the conclusions of CASAC and relied
on the evidence and information presented in the proposal. As such,
similar to CASAC, the rationale offered by these commenters was
consistent with that presented in the proposal to support the
Administrator's proposed decision to revise the current NO2
NAAQS.
Some industry commenters (e.g., Alliance of Automobile
Manufacturers (AAM), American Petroleum Institute (API), Interstate
Natural Gas Association of America (INGAA), Utility Air Regulatory
Group (UARG)) and one State commenter (IN Department of Environmental
Management) expressed support for retaining the current annual standard
alone. In supporting this view, these commenters generally concluded
that the current standard is requisite to protect public health with an
adequate margin of safety and that the available evidence is not
sufficient to support revision of the standard. For example, UARG
stated that ``EPA has failed to demonstrate that the present
NO2 NAAQS is no longer at the level requisite to protect
public health with an adequate margin of safety.'' In addition, INGAA
stated that
``* * * EPA should be compelled to retain the current standard and
defer a decision on a new short-term standard until the science is more
clearly defined.''
In support of their views, these commenters provided specific
comments on the epidemiologic and controlled human exposure evidence as
discussed below. In responding to these specific comments, we note that
the Administrator relied in the proposal on the evidence, information
and judgments contained in the ISA and the
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REA (including the policy assessment chapter) as well as on the advice
of CASAC. In considering the evidence, information, and judgments of
the ISA and the REA, the Agency notes that these documents have been
reviewed extensively by CASAC and have been discussed by CASAC at
multiple public meetings (see section I.D). In their letter to the
Administrator regarding the second draft ISA (Henderson, 2008), CASAC
noted the following:
Panel members concur with the primary conclusions reached in the
ISA with regard to health risks that are associated with
NO2 exposure. In particular, the Panel agrees with the
conclusion that the current scientific evidence is ``sufficient to
infer a likely causal relationship between short-term NO2
exposure and adverse effects on the respiratory system.'' The
strongest evidence in support of this conclusion comes from
epidemiology studies that show generally positive associations
between NO2 and respiratory symptoms, hospitalizations or
emergency department visits, as summarized in Figure 5.3.1.''
Similarly, in their letter to the Administrator on the final REA
(Samet, 2008b), CASAC noted the following:
Overall, CASAC found this version of the REA satisfactory in its
approach to moving from the scientific foundation developed in the
Integrated Science Assessment (ISA) to setting out evidence-based
options for the NAAQS. The REA provides the needed bridge from the
evidence presented in the ISA to a characterization of the exposures
and the associated risks with different profiles of exposure. It
draws on toxicological and epidemiological evidence and addresses
risk to an identified susceptible population, people with asthmatic
conditions. EPA has also systematically described uncertainties
associated with the risk assessments. We commend EPA for developing
a succinct and thoughtfully developed synthesis in chapter 10. This
summary chapter represents a long-needed and transparent model for
linking a substantial body of scientific evidence to the four
elements of the NAAQS.
Therefore, in discussing comments on the interpretation of the
scientific evidence and exposure/risk information, we note that CASAC
has endorsed the approaches and conclusions of the ISA and the REA.
These approaches and conclusions are discussed below in more detail,
within the context of specific public comments.
a. Comments on EPA's Interpretation of the Epidemiologic Evidence
Several industry groups (e.g., API, National Mining Association
(NMA), American Chemistry Council (ACC), AAM, Annapolis Center for
Science-Based Public Policy (ACSBPP), Engine Manufacturers Association
(EMA), ExxonMobil (Exxon), National Association of Manufacturers (NAM))
commented that, given the presence of numerous co-pollutants in the
air, epidemiologic studies do not support the contention that
NO2 itself is causing health effects.
While EPA has recognized that multiple factors can contribute to
the etiology of respiratory disease and that more than one air
pollutant could independently impact respiratory health, we continue to
judge, as discussed in the ISA, that the available evidence supports
the conclusion that there is an independent effect of NO2 on
respiratory morbidity. In reaching this judgment, we recognize that a
major methodological issue affecting NO2 epidemiologic
studies concerns the evaluation of the extent to which other air
pollutants may confound or modify NO2-related effect
estimates. The use of multipollutant regression models is the most
common approach for controlling potential confounding by co-pollutants
in epidemiologic studies. The issues related to confounding and the
evidence of potential confounding by co-pollutants has been thoroughly
reviewed in the ISA (see Figures 3.1-10 and 3.1-11) and in previous
assessments (e.g., the criteria document for PM) (EPA, 2004).
NO2 risk estimates for respiratory morbidity endpoints, in
general, were not sensitive to the inclusion of co-pollutants,
including particulate and gaseous pollutants. As observed in Figures
3.1-10 and 3.1-11 in the ISA, relative risks for hospital admissions or
emergency department visits are generally unchanged, nor is their
interpretation modified, upon inclusion of PM or gaseous co-pollutants
in the models. Similarly, associations between short-term
NO2 exposure and asthma symptoms are generally robust to
adjustment for co-pollutants in multipollutant models, as shown in
Figures 3.1-5 and 3.1-7 of the ISA. These results, in conjunction with
the results of a randomized intervention study evaluating respiratory
effects of indoor exposure to NO2 (ISA, section 3.1.4.1),
led to the conclusion that the effect of NO2 on respiratory
health outcomes is robust and independent of the effects of other
ambient co-pollutants.
In addition, experimental studies conducted in animals and humans
provide support for the plausibility of the associations reported in
epidemiologic studies. These controlled human exposure and animal
toxicological studies have reported effects of NO2 on immune
system function, lung host defense, airway inflammation, and airway
responsiveness (ISA, section 5.4). These experimental study results
support an independent contribution of NO2 to the
respiratory health effects reported in epidemiologic studies (ISA
Section 5.4).
In considering the entire body of evidence, including epidemiologic
and experimental studies, the ISA (section 5.4, p. 5-16) concluded the
following:
Although this [presence of co-pollutants] complicates the
efforts to disentangle specific NO2-related health
effects, the evidence summarized in this assessment indicates that
NO2 associations generally remain robust in multi-
pollutant models and supports a direct effect of short-term
NO2 exposure on respiratory morbidity at ambient
concentrations below the current NAAQS. The robustness of
epidemiologic findings to adjustment for co-pollutants, coupled with
data from animal and human experimental studies, support a
determination that the relationship between NO2 and
respiratory morbidity is likely causal, while still recognizing the
relationship between NO2 and other traffic-related
pollutants.
Comments on specific epidemiologic studies are discussed below.
The National Association of Manufacturers (NAM) commented that the
final REA relied on an epidemiologic study (Delfino et al. 2002) not
critically reviewed in the final ISA. Contrary to NAM's contention, the
study by Delfino et al. (2002) was critically reviewed by EPA staff and
pertinent information was extracted from the study. The respiratory
health effects of NO2 on asthma reported in this study are
included in Figure 5.3-1, Table 5.4-1, and Annex Table AX6.3-2 of the
ISA. While NAM comments on the narrative discussion of this study in
the final ISA, their contention that EPA scientists did not critically
analyze the study while preparing the final ISA is incorrect. The
inclusion of the study in the figures and tables in this ISA, as well
as inclusion in the 2004 PM AQCD, indicate critical analysis of the
study that was implemented throughout the review process. The narrative
discussion in the ISA focused on multicity studies (specifically those
by Schwartz et al. 1994, Mortimer et al. 2002 and Schildcrout et al.
2006), which provide substantial epidemiologic evidence for the
respiratory health effects of NO2 on asthma among children.
Additional comments from NAM contend that EPA's interpretation of
three individual epidemiologic studies (e.g. Krewski et al. 2000;
Schildcrout et al. 2006; Mortimer et al. 2002) is inconsistent across
different NAAQS reviews. The NAM comments on all three studies are
discussed below.
NAM stated the following regarding the study by Krewski et al:
In the Final ISA, EPA cites the Krewski, et al. (2000) study as
evidence of a significant
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association between NO2 exposure and mortality. Although
EPA acknowledges that exposure to NO2 was ``highly
correlated'' with other pollutants, including PM2.5 and
SO2, EPA does not consider the analysis of the respective
contributions of single pollutants in the same study that EPA
included in its prior Staff Paper for Particulate Matter. In that
document, EPA stated: ``In single-pollutant models, none of the
gaseous co-pollutants was significantly associated with mortality
except SO2.'' If EPA has not altered its scientific views
concerning this study as expressed in the PM Staff Paper, it is
entirely inappropriate for EPA to suggest that the Krewski, et al.
(2000) study provides any evidence of an association between
NO2 exposure and mortality.
In these comments, NAM fails to recognize that the report from Krewski
et al. (2000) contains a reanalysis of two cohort studies, the Harvard
Six Cities and the American Cancer Society (ACS) studies. The
characterization in the NOX ISA of the study by Krewski et
al. (2000), referenced by NAM in their comments, refers to the
reanalysis of the Harvard Six Cities Study. As stated in the
NOX ISA (p. 3-74):
Krewski et al. (2000) conducted a sensitivity analysis of the
Harvard Six Cities study and examined associations between gaseous
pollutants (i.e., O3, NO2, SO2, CO)
and mortality. NO2 showed risk estimates similar to those
for PM2.5 per ``low to high'' range increment with total
(1.15 [95% CI: 1.04, 1.27] per 10-ppb increase), cardiopulmonary
(1.17 [95% CI: 1.02, 1.34]), and lung cancer (1.09 [95% CI: 0.76,
1.57]) deaths; however, in this dataset NO2 was highly
correlated with PM2.5 (r = 0.78), SO4 2- (r =
0.78), and SO2 (r = 0.84).
In contrast, the characterization in the PM Staff Paper (EPA, 2005) of
the study by Krewski et al. (2000), referenced by NAM in their
comments, refers to the results of the ACS study. Therefore, NAM
appears to have confused the conclusions on the results of the
reanalysis of the Harvard Six Cities Study in the NOX ISA
with the conclusions on the results of the reanalysis of the ACS study
in the PM Staff Paper.
Further, in considering the reanalysis of the ACS study by Krewski
et al. (2000), the NOX ISA observed that ``NO2
showed no associations with mortality outcomes'' (ISA, p. 3-74). This
statement is consistent with the interpretation of that reanalysis as
discussed in the PM Staff Paper. Thus, there is no inconsistency in the
interpretation of the results of the study by Krewski et al. (2000) in
the PM Staff Paper (EPA, 2005) and the NOX ISA (EPA, 2008a).
NAM also commented that EPA has relied on a study by Schildcrout et
al. (2006) in the NOX ISA but declined to rely on the same
study for the previous review of the O3 NAAQS. NAM made the
following comment regarding the study by Schildcrout et al:
Another example of how EPA has reached different scientific
conclusions in the Final ISA than in prior NAAQS documents is
provided by the Schildcrout, et al. (2006) study. In the Final ISA,
EPA includes an extensive discussion of this study of asthmatic
children and the relationship purportedly found in this study
between NO2 and various respiratory symptoms. In
contrast, as part of the NAAQS review for ozone, EPA expressly
declined to rely on this same study because of specific limitations
in the study design. Among the limitations EPA cites were the fact
that the Schildcrout, et al. (2006) study included ``children in
which the severity of their asthma was not clearly identified,'' and
the use of a study population that was ``not comparable to other
large multi-city studies.'' EPA must explain why it chose to
discount the value of the Schildcrout, et al. (2006) study when
evaluating the effects of ozone, but has relied on it extensively in
the Final ISA for NO2.
The study by Schildcrout et al. (2006) appeared in the peer-review
literature too late to be considered in the 2006 O3 AQCD;
however, this study was included in the O3 Provisional
Assessment. The purpose of the Provisional Assessment was to determine
if new literature materially changed any of the broad scientific
conclusions regarding the health effects of O3 exposure as
stated in the 2006 O3 AQCD. EPA concluded that, taken in
context, the ``new'' information and findings did not materially change
any of the broad scientific conclusions regarding the health effects of
O3 exposure made in the O3 AQCD. Therefore, NAM's
contention that EPA ``declined'' to rely on the Schildcrout study for
the O3 review because of limitations in study design is not
correct.
The observations NAM draws from the O3 Provisional
Assessment regarding severity of asthma and the study population do not
indicate limitations that resulted in EPA ``discounting'' the study
results. Rather, these observations were intended to put the study in
perspective for purposes of interpreting the results within the context
of the larger body of O3 health effects evidence. These
observations were drawn from comments submitted by Dr. Schildcrout
regarding the interpretation of the results of his study in the
decision to revise the ozone standards (see docket ID EPA-HQ-OAR-2005-
0172-6991). The results of this study are being fully considered in the
ongoing review of the ozone NAAQS.
Finally, NAM contends that EPA reached differing scientific
conclusions on the use of self-reported peak expiratory flow (PEF)
depending on regulatory context, particularly in the large multi-city
trial by Mortimer et al. (2002). We disagree with this contention. EPA
consistently examines clinical measurements of lung function, which
include PEF, forced expiratory flow in 1 second (FEV1),
forced vital capacity (FVC), maximal midexpiratory flow (MMEF), maximal
expiratory flow at 50% (MEF50), maximal expiratory flow at
25% (MEF25), and forced expiratory flow at 25 to 75% of FVC
(FEF25-75). Evidence for all of these clinical measurements
is considered before drawing a conclusion related to the association of
lung function with a criteria pollutant. In different reviews, there
may be more evidence from one of these clinical measurements than
another. In the previous review of the O3 NAAQS, EPA
identified statistically significant associations between increased
ozone levels and morning PEF, which remained significant even when
concentrations exceeding 0.08 ppm were excluded from the analysis
(Mortimer et al. 2002). EPA considered this evidence, along with
evidence of other clinical measurements of changes in lung function, in
drawing conclusions on the relationship between ozone and lung
function. Using a similar approach to weigh the evidence pertinent to
lung function, including studies that produced no statistically
significant results for PEF, the NOX ISA (section 3.1.5.3)
states:
In summary, epidemiologic studies using data from supervised
lung function measurements (spirometry or peak flow meters) report
small decrements in lung function (Hoek and Brunekreef, 1994; Linn
et al., 1996; Moshammer et al., 2006; Peacock et al., 2003;
Schindler et al., 2001). No significant associations were reported
in any studies using unsupervised, self-administered peak flow [PEF]
measurements with portable devices.
The evaluation of the evidence in the NOX ISA is consistent
with the way the evidence from multiple clinical measures of lung
function was used in the review of the O3 NAAQS.
b. Comments on EPA's Interpretation of the Controlled Human Exposure
Evidence
A number of industry groups (e.g., AAM, ACC, API, Dow Chemical
Company (Dow), EMA, NAM, UARG) disagreed with EPA's reliance on a meta-
analysis of controlled human exposure studies of airway responsiveness
in asthmatics. Based on this meta-analysis (ISA, Table 3.1-3 for
results), the ISA concluded that ``small but significant increases in
nonspecific airway hyperresponsiveness were
[[Page 6487]]
observed * * * at 0.1 ppm NO2 for 60-min exposures in
asthmatics'' (ISA, p. 5-11). Industry groups raised a number of
objections to this analysis and the way in which it has been used in
the current review.
Several of these industry groups concluded that, in relying on this
analysis, EPA has inappropriately relied on a new unpublished meta-
analysis that has not been peer-reviewed, was not reviewed by CASAC,
and was not conducted in a transparent manner. For example, as part of
a Request for Correction submitted under EPA's Information Quality
Guidelines, NAM stated that ``EPA's substantial reliance on an
unpublished assessment described as a ``meta-analysis'' of the relation
between NO2 exposure and changes in airway responsiveness
violates EPA Guidelines requiring ``transparency about data and
methods.''
EPA disagrees with this characterization of the updated meta-
analysis included in the final ISA. As described in the ISA (p. 3-16),
this meta-analysis is based on an earlier analysis by Folinsbee (1992)
that has been subject to peer-review, that was published in a
scientific journal (Toxicol Ind Health. 8:1-11, 1992), and that was
reviewed by CASAC as part of the previous review of the NO2
NAAQS (EPA, 1993, Table 15-10). The updates to this earlier analysis
did not include substantive changes to the approach. As discussed in
the final ISA (p. 3-16), the changes made to the analysis were to
remove the results of one allergen study and add results from a non-
specific responsiveness study, which focused the meta-analysis on non-
specific airway responsiveness, and to discuss results for an
additional exposure concentration (i.e., 100 ppb). The information
needed to reproduce this meta-analysis is provided in the ISA (Tables
3.1-2 and 3.1-3, including footnotes).
While the ISA meta-analysis reports findings on airway
responsiveness in asthmatics following exposure to 100 ppb
NO2, a concentration not specifically discussed in the
findings of the original report by Folinsbee (1992), this does not
constitute a substantive change to that original analysis. For
exposures at rest, four of the studies included in the analysis by
Folinsbee evaluated the effects of exposure to 100 ppb NO2.
In that original meta-analysis, these studies were grouped with another
study that evaluated exposures to 140 ppb NO2. When analyzed
together, exposures to NO2 concentrations of 100 ppb and 140
ppb (grouped together in the manuscript and described as less than 0.2
ppm) increased airway responsiveness in 65% of resting asthmatics (p <
0.01). Therefore, reporting results at 100 ppb NO2 in the
ISA meta-analysis reflects a change in the way the data are presented
and does not reflect a substantive change to the study. This change in
presentation allows specific consideration of the potential for
exposures to 100 ppb NO2 to increase airway responsiveness,
rather than grouping results at 100 ppb with results at other exposure
concentrations.
In addition, the updated meta-analysis was considered by CASAC
during their review of the REA (REA, Table 4-5 reports the results of
the updated meta-analysis), which based part of the assessment of
NO2-associated health risks on the results of the meta-
analysis. In their letter to the Administrator on the final REA (Samet,
2008b), CASAC stated that ``[t]he evidence reviewed in the REA
indicates that adverse health effects have been documented in clinical
studies of persons with asthma at 100 ppb'' and that ``CASAC firmly
recommends that the upper end of the range [of standard levels] not
exceed 100 ppb, given the findings of the REA.'' In addition, in their
comments on the proposal, CASAC reiterated this advice in their
statement that ``the level of the one-hour NO2 standard
should be within the range of 80-100 ppb and not above 100 ppb.'' These
statements indicate that CASAC did specifically consider the results of
the updated meta-analysis and that they used those results to inform
their recommendations on the range of standard levels supported by the
scientific evidence.
In summary, we note the following:
The original meta-analysis was published in a peer-
reviewed journal and was reviewed by CASAC in the previous review of
the NO2 NAAQS.
The updated meta-analysis does not include substantive
changes to the methodology of this original analysis.
The changes that were made are clearly described in the
ISA.
CASAC specifically reviewed and considered the ISA meta-
analysis in making recommendations regarding the range of standard
levels supported by the science.
Many of these same industry groups also referred in their comments
to a recent meta-analysis of controlled human exposure studies
evaluating the airway response in asthmatics following NO2
exposure (Goodman et al., 2009). These groups generally recommended
that EPA rely on this meta-analysis and on the authors' conclusions
with regard to NO2 and airway responsiveness. Specific
comments based on the manuscript by Goodman et al., as well as EPA's
responses, are discussed below in more detail.\9\
---------------------------------------------------------------------------
\9\ EPA considers the Goodman study to be a ``new study'' on
which, as discussed above in section 1.B, it would not be
appropriate to base a standard in the absence of thorough CASAC and
public review of the study and its methodology. However, as
discussed below, EPA has considered the study in the context of
responding to public comments on the proposal and has concluded it
does not provide a basis to materially change any of the broad
scientific conclusions regarding the health effects of
NO2 made in the air quality criteria.
---------------------------------------------------------------------------
Industry commenters generally claimed that the meta-analysis by
Goodman et al. supports the conclusion that no adverse effects occur
following exposures up to 600 ppb NO2. However, Table 4 of
the Goodman study reports that 64% (95% Confidence Interval: 58%, 71%)
of resting asthmatics exposed to NO2 experienced an increase
in airway responsiveness. Furthermore, Figure 2a of this manuscript
reports that for exposures < 0.2 ppm, the fraction affected is 0.61
(95% CI: 0.52, 0.70) while for exposures of 0.2 ppm to < 0.3 ppm, the
fraction affected is 0.66 (95% CI: 0.59, 0.74). These findings are
consistent with those reported in the meta-analysis by Folinsbee and in
the updated meta-analysis that was included in the final ISA.
Also based on the meta-analysis by Goodman et al. (2009), several
industry commenters concluded that NO2-induced airway
hyperresponsiveness is not adverse and, therefore, should not be
considered in setting standards. The basis for this comment appears to
be the conclusions reached by Goodman et al. that there is no dose-
response relationship for NO2 and that the magnitude of any
NO2 effect on airway responsiveness is too small to be
considered adverse.
Due to differences in study protocols in the NO2-airway
response literature (ISA, section 3.1.3), EPA disagrees with the
approach taken in the Goodman study to use existing data to attempt to
evaluate the presence of a dose-response relationship and to determine
the magnitude of the NO2 response. Examples of differences
in the study protocols include the NO2 exposure method
(i.e., mouthpiece versus chamber), subject activity level (i.e., rest
versus exercise) during NO2 exposure, choice of airway
challenge agent, and physiological endpoint used to quantify airway
responses. Goodman et al. (2009) also recognized heterogeneity among
studies as a limitation in their analyses.
As a result of these differences, EPA judged it appropriate in the
ISA meta-analysis to assess only the fraction of asthmatics
experiencing increased or decreased airway responsiveness
[[Page 6488]]
following NO2 exposure. We have acknowledged in the REA, the
proposal, and in this final rulemaking that there is uncertainty with
regard to the magnitude and the clinical-significance of
NO2-induced increases in airway responsiveness (see sections
II.C.3 and II.F.4.a in the proposed rulemaking as well as II.F.3 in
this final rulemaking). The REA stated the following (p. 302):
[O]ne of the important uncertainties associated with these
[NO2-induced airway hyperresponsiveness] results is that,
because the meta-analysis evaluated only the direction of the change
in airway responsiveness, it is not possible to discern the
magnitude of the change from these data. This limitation makes it
particularly difficult to quantify the public health implications of
these results.
While we acknowledge this uncertainty, EPA disagrees with the
conclusion that the NO2-induced increase in airway
responsiveness in asthmatics exposed to NO2 concentrations
up to 600 ppb is not adverse and should not be considered in setting
standards. Specifically, we note that the ISA concluded that
``[t]ransient increases in airway responsiveness following
NO2 exposure have the potential to increase symptoms and
worsen asthma control'' (ISA, section 5.4). The uncertainty over the
adversity of the response reported in controlled human exposure studies
does not mean that the NO2-induced increase in airway
responsiveness is not adverse. Rather, it means that there is a risk of
adversity, especially for asthmatics with more than mild asthma, but
that this risk cannot be fully characterized based on existing studies.
The studies of NO2 and airway responsiveness included in the
meta-analysis have generally evaluated mild asthmatics, rather than
more severely affected asthmatics who could be more susceptible to the
NO2-induced increase in airway responsiveness (ISA, section
3.1.3.2). Given that this is the case, and given the large percentage
of asthmatics that experienced an NO2-induced increase in
airway responsiveness in the studies and the large size of the
asthmatic population in the United States, the REA concluded that it is
appropriate to consider NO2-induced airway
hyperresponsiveness in characterizing NO2-associated health
risks (REA, section 10.3.2). As noted above, CASAC endorsed this
conclusion in their letters to the Administrator on the final REA and
on the proposal (Samet, 2008b; Samet, 2009).
c. Comments on EPA's Characterization of NO2-Associated
Exposures and Health Risks
Several commenters discussed the analyses of NO2-
associated exposures and health risks presented in the REA. As in past
reviews (EPA 2005, 2007c, 2007d), EPA has estimated allowable risks
associated with the current standard and potential alternative
standards to inform judgments on the public health risks that could
exist under different standard options. Some industry commenters (e.g.,
API, NMA) concluded that the Administrator should consider modeled
exposures and risks associated with actual NO2 air quality
rather than with NO2 concentrations adjusted to simulate
just meeting the current annual standard or potential alternative 1-
hour standards. These commenters pointed out that such simulations
require large adjustments to air quality and are highly uncertain and
that NAAQS are intended to address actual, rather than highly
improbable, risks to health.
We disagree with these commenters that exposure- and risk-related
considerations in the NAAQS review should rely only on unadjusted air
quality. In considering whether the current standard is requisite to
protect public health with an adequate margin of safety, air quality
adjustments allow estimates of NO2-related exposures and
health risks that could exist in areas that just meet that standard.
That is, these adjustments allow consideration of exposures and risks
that would be permissible under the current standard. Therefore, such
adjustments are clearly useful to inform a decision on the issue before
EPA (i.e., the adequacy of the level of public health protection
associated with allowable NO2 air quality under the
standard). Similarly, air quality adjustments to simulate different
potential alternative standards provide information on exposures and
risks that would be permissible under these alternatives.\10\ As noted
above, in their letter to the Administrator on the final REA (Samet,
2008b), CASAC concluded that ``The REA provides the needed bridge from
the evidence presented in the ISA to a characterization of the
exposures and the associated risks with different profiles of
exposure.''
---------------------------------------------------------------------------
\10\ Once EPA determines whether to retain or revise the current
standard, the actual air quality levels in various areas of the
country are clearly relevant under the NAAQS implementation
provisions for the Act, such as the provision for designation of
areas based on whether or not they attain the required NAAQS.
---------------------------------------------------------------------------
We agree that there are uncertainties inherent in air quality
adjustments. These uncertainties are discussed thoroughly in the REA
(sections 7.4, 8.12, 9.6, and 10.3.2.1) and in the proposed rule
(section II.C.3). For example, the policy assessment chapter of the REA
(section 10.3.2.1) noted the following regarding adjustment of
NO2 concentrations:
In order to simulate just meeting the current annual standard
and many of the alternative 1-h standards analyzed, an upward
adjustment of recent ambient NO2 concentrations was
required. We note that this adjustment does not reflect a judgment
that levels of NO2 are likely to increase under the
current standard or any of the potential alternative standards under
consideration. Rather, these adjustments reflect the fact that the
current standard, as well as some of the alternatives under
consideration, could allow for such increases in ambient
NO2 concentrations. In adjusting air quality to simulate
just meeting these standards, we have assumed that the overall shape
of the distribution of NO2 concentrations would not
change. While we believe this is a reasonable assumption in the
absence of evidence supporting a different distribution and we note
that available analyses support this approach (Rizzo, 2008), we
recognize this as an important uncertainty. It may be an especially
important uncertainty for those scenarios where considerable upward
adjustment is required to simulate just meeting one or more of the
standards.
These air quality adjustments are not meant to imply an expectation
that NO2 concentrations will increase broadly across the
United States or in any given area (REA, section 10.3.2.1). Rather, as
noted above, they are meant to estimate NO2-related
exposures and health risks that would be permitted under the current
and potential alternative standards. Such estimates can inform
decisions on whether the current standard, or particular potential
alternative standards, provide the requisite protection of public
health.
3. Conclusions Regarding the Adequacy of the Current Standard
In considering the adequacy of the current standard, the
Administrator has considered the scientific evidence assessed in the
ISA, the exposure and risk results presented in the REA, the
conclusions of the policy assessment chapter of the REA, and comments
from CASAC and the public. These considerations are described below.
In considering the scientific evidence as it relates to the
adequacy of the current standard, the Administrator notes that the
epidemiologic evidence has grown substantially since the last review
with the addition of field and panel studies, intervention studies, and
time-series studies of effects such as emergency department visits and
hospital admissions associated with
[[Page 6489]]
short-term NO2 exposures. No epidemiologic studies were
available in 1993 assessing relationships between NO2 and
outcomes such as hospital admissions or emergency department visits. In
contrast, dozens of epidemiologic studies on such outcomes, conducted
at recent and current ambient NO2 concentrations, are now
included in this evaluation (ISA, chapter 3).
As an initial consideration with regard to the adequacy of the
current standard, the Administrator notes that the evidence relating
long-term (weeks to years) NO2 exposures at current ambient
concentrations to adverse health effects was judged in the ISA to be
either ``suggestive but not sufficient to infer a causal relationship''
(respiratory morbidity) or ``inadequate to infer the presence or
absence of a causal relationship'' (mortality, cancer, cardiovascular
effects, reproductive/developmental effects) (ISA, sections 5.3.2.4-
5.3.2.6). In contrast, the evidence relating short-term (minutes to
hours) NO2 exposures to respiratory morbidity was judged to
be ``sufficient to infer a likely causal relationship'' (ISA, section
5.3.2.1). This conclusion was supported primarily by a large body of
recent epidemiologic studies that evaluated associations of short-term
NO2 concentrations with respiratory symptoms, emergency
department visits, and hospital admissions. Given these conclusions
from the ISA, the Administrator judges that, at a minimum,
consideration of the adequacy of the current annual standard should
take into account the extent to which that standard provides protection
against respiratory effects associated with short-term NO2
exposures.
In considering the NO2 epidemiologic studies as they
relate to the adequacy of the current standard, the Administrator notes
that annual average NO2 concentrations were below the level
of the current annual NO2 NAAQS in many of the locations
where positive, and often statistically significant, associations with
respiratory morbidity endpoints have been reported (ISA, section 5.4).
As discussed previously, the ISA characterized that evidence for
respiratory effects as consistent and coherent. The evidence is
consistent in that associations are reported in studies conducted in
numerous locations and with a variety of methodological approaches
(ISA, section 5.3.2.1). It is coherent in the sense that the studies
report associations with respiratory health outcomes that are logically
linked together (ISA, section 5.3.2.1). The ISA noted that when the
epidemiologic literature is considered as a whole, there are generally
positive associations between NO2 and respiratory symptoms,
hospital admissions, and emergency department visits. A number of these
associations are statistically significant, particularly the more
precise effect estimates (ISA, section 5.3.2.1).
As discussed in the proposal (II.E.1) and above, the Administrator
acknowledges that the interpretation of these NO2
epidemiologic studies is complicated by the fact that on-road vehicle
exhaust emissions are a nearly ubiquitous source of combustion
pollutant mixtures that include NO2. She notes that, in
order to provide some perspective on the uncertainty related to the
presence of co-pollutants the ISA evaluated epidemiologic studies that
employed multi-pollutant models, epidemiologic studies of indoor
NO2 exposure, and experimental studies. Specifically, the
ISA noted that a number of NO2 epidemiologic studies have
attempted to disentangle the effects of NO2 from those of
co-occurring pollutants by employing multi-pollutant models. When
evaluated as a whole, NO2 effect estimates in these models
generally remained robust when co-pollutants were included. Therefore,
despite uncertainties associated with separating the effects of
NO2 from those of co-occurring pollutants, the ISA (section
5.4, p. 5-16) concluded that ``the evidence summarized in this
assessment indicates that NO2 associations generally remain
robust in multi-pollutant models and supports a direct effect of short-
term NO2 exposure on respiratory morbidity at ambient
concentrations below the current NAAQS.'' With regard to indoor
studies, the ISA noted that these studies can test hypotheses related
to NO2 specifically (ISA, section 3.1.4.1). Although
confounding by indoor combustion sources is a concern, indoor studies
are not confounded by the same mix of co-pollutants present in the
ambient air or by the contribution of NO2 to the formation
of secondary particles or O3 (ISA, section 3.1.4.1). The ISA
noted that the findings of indoor NO2 studies are consistent
with those of studies using ambient concentrations from central site
monitors and concluded that indoor studies provide evidence of
coherence for respiratory effects (ISA, section 3.1.4.1). With regard
to experimental studies, the REA noted that they have the advantage of
providing information on health effects that are specifically
associated with exposure to NO2 in the absence of co-
pollutants. The ISA concluded that the NO2 epidemiologic
literature is supported by (1) evidence from controlled human exposure
studies of airway hyperresponsiveness in asthmatics, (2) controlled
human exposure and animal toxicological studies of impaired host-
defense systems and increased risk of susceptibility to viral and
bacterial infection, and (3) controlled human exposure and animal
toxicological studies of airway inflammation (ISA, section 5.3.2.1 and
5.4). Given the above consideration of the evidence, particularly the
epidemiologic studies reporting NO2-associated health
effects in locations that meet the current standard, the Administrator
agrees with the conclusion in the policy assessment chapter of the REA
that the scientific evidence calls into question the adequacy of the
current standard to protect public health.
In addition to the evidence-based considerations described above,
the Administrator has considered the extent to which exposure- and
risk-based information can inform decisions regarding the adequacy of
the current annual NO2 standard. While she acknowledges the
uncertainties associated with adjusting air quality in these analyses,
she judges that such analyses are appropriate for consideration in this
review of the NO2 primary NAAQS. In reaching this conclusion
she notes the considerations discussed above, particularly the
endorsement by CASAC of the REA and its characterization of
NO2-associated exposures and health risks.
In considering the exposure- and risk-based information with regard
to the adequacy of the current annual NO2 standard to
protect the public health, the Administrator notes the conclusion in
the policy assessment chapter of the REA that risks estimated to be
associated with air quality adjusted upward to simulate just meeting
the current standard can reasonably be concluded to be important from a
public health perspective. In particular, a large percentage (8-9%) of
respiratory-related ED visits in Atlanta could be associated with
short-term NO2 exposures, most asthmatics in Atlanta could
be exposed on multiple days per year to NO2 concentrations
at or above 300 ppb, and most locations evaluated could experience on-/
near-road NO2 concentrations above 100 ppb on more than half
of the days in a given year. Therefore, after considering the results
of the exposure and risk analyses presented in the REA the
Administrator agrees with the conclusion of the policy assessment
chapter of the REA that exposure- and risk-based results reinforce the
scientific evidence in
[[Page 6490]]
supporting the conclusion that consideration should be given to
revising the current standard so as to provide increased public health
protection, especially for at-risk groups, from NO2-related
adverse health effects associated with short-term, and potential long-
term, exposures.
In reaching a conclusion on the adequacy of the current standard,
the Administrator has also considered advice received from CASAC. In
their comments on the final REA, CASAC agreed that the primary concern
in this review is to protect against health effects that have been
associated with short-term NO2 exposures. CASAC also agreed
that the current annual standard is not sufficient to protect public
health against the types of exposures that could lead to these health
effects. As noted in their letter to the EPA Administrator, ``CASAC
concurs with EPA's judgment that the current NAAQS does not protect the
public's health and that it should be revised'' (Samet, 2008b).
Based on the considerations discussed above, the Administrator
concludes that the current NO2 primary NAAQS alone is not
requisite to protect public health with an adequate margin of safety.
Accordingly, she concludes that the NO2 primary standard
should be revised in order to provide increased public health
protection against respiratory effects associated with short-term
exposures, particularly for susceptible populations such as asthmatics,
children, and older adults. In considering approaches to revising the
current standard, the Administrator concludes that it is appropriate to
consider setting a new short-term standard (see below). The
Administrator notes that such a short-term standard could provide
increased public health protection, especially for members of at-risk
groups, from effects described in both epidemiologic and controlled
human exposure studies to be associated with short-term exposures to
NO2.
F. Elements of a New Short-Term Standard
In considering a revised NO2 primary NAAQS, the
Administrator notes the need to protect at-risk individuals from short-
term exposures to NO2 air quality that could cause the types
of respiratory morbidity effects reported in epidemiologic studies and
the need to protect at-risk individuals from short-term exposure to
NO2 concentrations reported in controlled human exposure
studies to increase airway responsiveness in asthmatics. The
Administrator's considerations with regard to her decisions are
discussed in the following sections in terms of indicator (II.F.1),
averaging time (II.F.2), level (II.F.3), and form (II.F.4).
1. Indicator
a. Rationale for Proposed Decision
In past reviews, EPA has focused on NO2 as the most
appropriate indicator for ambient NOX. In making a decision
in the current review on the most appropriate indicator, the
Administrator considered the conclusions of the ISA and the policy
assessment chapter of the REA as well as the view expressed by CASAC.
The policy assessment chapter of the REA noted that, while the presence
of NOX species other than NO2 has been
recognized, no alternative to NO2 has been advanced as being
a more appropriate surrogate. Controlled human exposure studies and
animal toxicology studies assessed in the ISA provide specific evidence
for health effects following exposure to NO2. Epidemiologic
studies also typically report levels of NO2 though the
degree to which monitored NO2 reflects actual NO2
levels, as opposed to NO2 plus other gaseous NOX,
can vary (REA, section 2.2.3). In addition, because emissions that lead
to the formation of NO2 generally also lead to the formation
of other NOX oxidation products, measures leading to
reductions in population exposures to NO2 can generally be
expected to lead to reductions in population exposures to other gaseous
NOX. Therefore, an NO2 standard can also be
expected to provide some degree of protection against potential health
effects that may be independently associated with other gaseous
NOX even though such effects are not discernable from
currently available studies indexed by NO2 alone. Given
these key points, the policy assessment chapter of the REA concluded
that the evidence supports retaining NO2 as the indicator.
Consistent with this conclusion, the CASAC Panel stated in its letter
to the EPA Administrator that it ``concurs with retention of
NO2 as the indicator'' (Samet, 2008b). In light of the above
considerations, the Administrator proposed to retain NO2 as
the indicator in the current review.
b. Comments on Indicator
A relatively small number of comments directly addressed the issue
of the indicator for the standard (CASAC, Dow, API, AAM, and the
Missouri Department of Natural Resources Air Pollution Control Program
(MODNR)). All of these commenters endorsed the proposal to continue to
use NO2 as the indicator for ambient NOX.
c. Conclusions on Indicator
Based on the available information discussed above, and consistent
with the views of CASAC and other commenters, the Administrator
concludes that it is appropriate to continue to use NO2 as
the indicator for a standard that is intended to address effects
associated with exposure to NO2, alone or in combination
with other gaseous NOX. In so doing, the Administrator
recognizes that measures leading to reductions in population exposures
to NO2 will also reduce exposures to other nitrogen oxides.
2. Averaging Time
This section discusses considerations related to the averaging time
of the NO2 primary NAAQS. Specifically, this section
summarizes the rationale for the Administrator's proposed decision
regarding averaging time (II.F.2.a; see section II.F.2 of the proposal
for more detail), discusses comments related to averaging time
(II.F.2.b), and presents the Administrator's final conclusions
regarding averaging time (II.F.2.c).
a. Rationale for Proposed Decision
In considering the most appropriate averaging time for the
NO2 primary NAAQS, the Administrator noted in the proposal
the conclusions and judgments made in the ISA about available
scientific evidence, air quality correlations discussed in the REA,
conclusions of the policy assessment chapter of the REA, and CASAC
recommendations (section II.F.2 in the proposal). Specifically, she
noted the following:
Experimental studies in humans and animals have reported
respiratory effects following NO2 exposures lasting from
less than 1-hour up to several hours. Epidemiologic studies have
reported associations between respiratory effects and both 1 hour and
24-hour NO2 concentrations. Therefore, the experimental
evidence provides support for an averaging time of shorter duration
than 24 hours (e.g., 1 hour) while the epidemiologic evidence provides
support for both 1-hour and 24-hour averaging times. At a minimum, this
suggests that a primary concern with regard to averaging time is the
level of protection provided against 1-hour NO2
concentrations.
Air quality correlations presented in the policy
assessment chapter of the REA illustrated the relatively high degree of
variability in the ratios of annual average to short-term
NO2 concentrations (REA, Table 10-2). This
[[Page 6491]]
variability suggests that a standard based on annual average
NO2 concentrations would not likely be an effective or
efficient approach to focus protection on short-term exposures.
These air quality correlations (REA, Table 10-1) suggested
that a standard based on 1-hour daily maximum NO2
concentrations could also be effective at protecting against 24-hour
NO2 concentrations.
The policy assessment chapter of the REA concluded that
the scientific evidence, combined with the air quality correlations,
support the appropriateness of a standard based on 1-hour daily maximum
NO2 concentrations to protect against health effects
associated with short-term exposures.
CASAC concurred ``with having a short-term NAAQS primary
standard for oxides of nitrogen and using the one-hour maximum
NO2 value'' (Samet, 2008b).
Based on these considerations, the Administrator proposed to set a new
standard based on 1-hour daily maximum NO2 concentrations.
b. Comments on averaging time
As discussed above, CASAC endorsed the establishment of a new
standard with a 1-hour averaging time. CASAC stated the following in
their comments on the proposal (Samet, 2009):
In reviewing the REA, CASAC supported a short-term standard for
NO2 and in reviewing the proposal, CASAC supports the
proposed one-hour averaging time in EPA's proposed rule.
The supporting rationale offered by CASAC in support of a new 1-hour
standard was generally the same as that put forward in the final REA
and the proposal. Specifically, that rationale considered the available
scientific evidence, which supports a link between 1-hour
NO2 concentrations and adverse respiratory effects, and air
quality information presented in the REA, which suggests that a 1-hour
standard can protect against effects linked to short-term
NO2 exposures while an annual standard would not be an
effective or efficient approach to protecting against these effects.
A large number of public commenters also endorsed the establishment
of a new standard with a 1-hour averaging time. These included a number
of State agencies and organizations (e.g., NACAA, NESCAUM and agencies
in CA, IL, NM, TX, VA); environmental, medical, and public health
organizations (e.g., ACCP, ALA, AMA, ATS, CAC, EDF, EJ, GASP, NACPR,
NAMDRC, NRDC); and most individual commenters. The supporting
rationales offered by these commenters often acknowledged the
recommendations of CASAC and the Administrator's rationale as discussed
in the proposal.
Though many industry commenters recommended not revising the
current annual standard (as discussed above in section II.E.2), several
of these groups did conclude that if a short-term standard were to be
set, a 1-hour averaging time would be appropriate (e.g., Colorado
Petroleum Association (CPA), Dow, NAM, Petroleum Association of Wyoming
(PAW), Utah Petroleum Association (UPA)). As discussed above, industry
commenters who disagreed with setting a new 1-hour standard generally
based this conclusion on their interpretation of the scientific
evidence and their conclusion that this evidence does not support the
need to revise the current annual standard. These comments, and EPA's
responses, are discussed in more detail above (section II.E) and in the
Response to Comments document.
c. Conclusions on Averaging Time
In considering the most appropriate averaging time for the
NO2 primary NAAQS, the Administrator notes the available
scientific evidence as assessed in the ISA, the air quality analyses
presented in the REA, the conclusions of the policy assessment chapter
of the REA, CASAC recommendations, and public comments received. These
considerations are described below.
When considering averaging time, the Administrator notes that the
evidence relating short-term (minutes to hours) NO2
exposures to respiratory morbidity was judged in the ISA to be
``sufficient to infer a likely causal relationship'' (ISA, section
5.3.2.1) while the evidence relating long-term (weeks to years)
NO2 exposures to adverse health effects was judged to be
either ``suggestive but not sufficient to infer a causal relationship''
(respiratory morbidity) or ``inadequate to infer the presence or
absence of a causal relationship'' (mortality, cancer, cardiovascular
effects, reproductive/developmental effects) (ISA, sections 5.3.2.4-
5.3.2.6). Thus, the Administrator concludes that these judgments most
directly support an averaging time that focuses protection on short-
term exposures to NO2.
As in past reviews of the NO2 NAAQS, the Administrator
notes that it is instructive to evaluate the potential for a standard
based on annual average NO2 concentrations, as is the
current standard, to provide protection against short-term
NO2 exposures. To this end, the Administrator notes that
Table 10-1 in the REA reported the ratios of short-term to annual
average NO2 concentrations. Ratios of 1-hour daily maximum
concentrations (98th and 99th percentile \11\) to annual average
concentrations across 14 locations ranged from 2.5 to 8.7 while ratios
of 24-hour average concentrations to annual average concentrations
ranged from 1.6 to 3.8 (see Thompson, 2008 for more details). The
policy assessment chapter of the REA concluded that the variability in
these ratios across locations, particularly those for 1-hour
concentrations, suggested that a standard based on annual average
NO2 concentrations would not likely be an effective or
efficient approach to focus protection on short-term NO2
exposures. For example, in an area with a relatively high ratio (e.g.,
8), the current annual standard (53 ppb) would be expected to allow 1-
hour daily maximum NO2 concentrations of about 400 ppb. In
contrast, in an area with a relatively low ratio (e.g., 3), the current
standard would be expected to allow 1-hour daily maximum NO2
concentrations of about 150 ppb. Thus, for purposes of protecting
against the range of 1-hour NO2 exposures, the REA noted
that a standard based on annual average concentrations would likely
require more control than necessary in some areas and less control than
necessary in others, depending on the standard level selected.
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\11\ As discussed below, 98th and 99th percentile forms were
evaluated in the REA. A 99th percentile form corresponds
approximately to the 4th highest 1-hour concentration in a year
while a 98th percentile form corresponds approximately to the 7th or
8th highest 1-hour concentration in a year. A 4th highest
concentration form has been used previously in the O3
NAAQS while a 98th percentile form has been used previously in the
PM2.5 NAAQS.
---------------------------------------------------------------------------
In considering the level of support available for specific short-
term averaging times, the Administrator notes that the policy
assessment chapter of the REA considered evidence from both
experimental and epidemiologic studies. Controlled human exposure
studies and animal toxicological studies provide evidence that
NO2 exposures from less than 1-hour up to 3-hours can result
in respiratory effects such as increased airway responsiveness and
inflammation (ISA, section 5.3.2.7). Specifically, the ISA concluded
that NO2 exposures of 100 ppb for 1-hour (or 200 ppb to 300
ppb for 30-min) can result in small but significant increases in
nonspecific airway responsiveness (ISA, section 5.3.2.1). In contrast,
the epidemiologic literature provides support for short-term averaging
times ranging from approximately 1-hour up to 24-hours (ISA, section
5.3.2.7). A
[[Page 6492]]
number of epidemiologic studies have detected positive associations
between respiratory morbidity and 1-hour (daily maximum) and/or 24-hour
NO2 concentrations. A few epidemiologic studies have
considered both 1-hour and 24-hour averaging times, allowing
comparisons to be made. The ISA reported that such comparisons in
studies that evaluate asthma emergency department visits failed to
reveal differences between effect estimates based on a 1-hour averaging
time and those based on a 24-hour averaging time (ISA, section
5.3.2.7). Therefore, the ISA concluded that it is not possible, from
the available epidemiologic evidence, to discern whether effects
observed are attributable to average daily (or multi-day)
concentrations (24-hour average) or high, peak exposures (1-hour
maximum) (ISA, section 5.3.2.7).
As noted in the policy assessment chapter of the REA, given the
above conclusions, the experimental evidence provides support for an
averaging time of shorter duration than 24 hours (e.g., 1-h) while the
epidemiologic evidence provides support for both 1-hour and 24-hour
averaging times. The Administrator concludes that, at a minimum, this
suggests that a primary concern with regard to averaging time is the
level of protection provided against 1-hour NO2
concentrations. However, she also notes that it is important to
consider the ability of a 1-hour averaging time to protect against 24-
hour average NO2 concentrations. To this end, the
Administrator notes that Table 10-2 in the REA presented correlations
between 1-hour daily maximum NO2 concentrations and 24-hour
average NO2 concentrations (98th and 99th percentile) across
14 locations (see Thompson, 2008 for more detail). Typical ratios
ranged from 1.5 to 2.0, though one ratio (Las Vegas) was 3.1. These
ratios were far less variable than those discussed above for annual
average concentrations, suggesting that a standard based on 1-hour
daily maximum NO2 concentrations could also be effective at
protecting against 24-hour NO2 concentrations. The REA
concluded that the scientific evidence, combined with the air quality
correlations described above, support the appropriateness of a standard
based on 1-hour daily maximum NO2 concentrations to protect
against health effects associated with short-term exposures.
Based on these considerations, the Administrator concludes that a
standard with a 1-hour averaging time can effectively limit short-term
(i.e., 1- to 24-hours) exposures that have been linked to adverse
respiratory effects. This conclusion is based on the observations
summarized above and in more detail in the proposal, particularly that:
(1) The 1-hour averaging time has been directly associated with
respiratory effects in both epidemiologic and experimental studies and
that (2) results from air quality analyses suggest that a 1-hour
standard could also effectively control 24-hour NO2
concentrations. In addition, the Administrator notes the support
provided for a 1-hour averaging time in comments from CASAC, States,
environmental groups, and medical/public health groups. The
Administrator notes that arguments offered by some industry groups
against setting a 1-hour NO2 standard generally focus on
commenters' conclusions regarding uncertainties in the scientific
evidence. As discussed in more detail above (section II.E.2), the
Administrator disagrees with the conclusions of these commenters
regarding the appropriate interpretation of the scientific evidence and
associated uncertainties. Given these considerations, the Administrator
judges that it is appropriate to set a new NO2 standard with
a 1-hour averaging time.
3. Form
This section discusses considerations related to the form of the 1-
hour NO2 primary NAAQS. Specifically, this section
summarizes the rationale for the Administrator's proposed decision
regarding form (II.F.4.a; see section II.F.3 of the proposal for more
detail), discusses comments related to form (II.F.4.b), and presents
the Administrator's final conclusions regarding form (II.F.4.c).
a. Rationale For Proposed Decision
When considering alternative forms in the proposal, the
Administrator noted the conclusions in the policy assessment chapter of
the REA. Specifically, she noted the conclusion that the adequacy of
the public health protection provided by the combination of standard
level and form should be the foremost consideration. With regard to
this, she noted that concentration-based forms can better reflect
pollutant-associated health risks than forms based on expected
exceedances. This is the case because concentration-based forms give
proportionally greater weight to years when pollutant concentrations
are well above the level of the standard than to years when the
concentrations are just above the standard, while an expected
exceedance form would give the same weight to years with concentrations
that just exceed the standard as to years when concentrations greatly
exceed the standard. The Administrator also recognized the conclusion
in the policy assessment chapter of the REA that it is desirable from a
public health perspective to have a form that is reasonably stable and
insulated from the impacts of extreme meteorological events. With
regard to this, she noted that a form that calls for averaging
concentrations over three years would provide greater regulatory
stability than a form based on a single year of concentrations.
Therefore, consistent with recent reviews of the O3 and PM
NAAQS, the proposal focused on concentration-based forms averaged over
3 years, as evaluated in the REA.
In considering specific concentration-based forms, the REA focused
on 98th and 99th percentile concentrations averaged over 3 years. This
focus on the upper percentiles of the distribution is appropriate given
the reliance, in part, on NO2 health evidence from
experimental studies, which provide information on specific exposure
concentrations that are linked to specific health effects. The REA
noted that a 99th percentile form for a 1-hour daily maximum standard
would correspond approximately to the 4th highest daily maximum
concentration in a year (which is the form of the current O3
NAAQS) while a 98th percentile form (which is the form of the current
short-term PM2.5 NAAQS) would correspond approximately to
the 7th or 8th highest daily maximum concentration in a year (REA,
Table 10-4; see Thompson, 2008 for methods).
Consideration in the REA of an appropriate form for a 1-hour
standard was based on analyses of standard levels that reflected the
allowable area-wide NO2 concentration, not the maximum
allowable concentration. Therefore, in their review of the final REA,
CASAC did not have the opportunity to comment on the appropriateness of
specific forms in conjunction with a standard level that reflects the
maximum allowable NO2 concentration anywhere in an area.
Given this, when considering alternative forms for the 1-hour standard
in the proposal, the Administrator judged that it was appropriate to
consider both forms evaluated in the REA (i.e., 98th and 99th
percentiles). Therefore, she proposed to adopt either a 99th percentile
or a 4th highest form, averaged over 3 years, and she solicited comment
on both 98th percentile and 7th or 8th highest forms.
b. CASAC and Public Comments on Form
In their letter to the Administrator, CASAC discussed the issue of
form within the context of the proposed
[[Page 6493]]
approach of setting a 1-hour standard level that reflects the maximum
allowable NO2 concentration anywhere in an area. CASAC
recommended that, for such a standard, EPA adopt a form based on the 3-
year average of the 98th percentile of the distribution of 1-hour daily
maximum NO2 concentrations. Specifically, they stated the
following in their comments on the proposal (Samet, 2009):
The 98th percentile is preferred by CASAC for the form, given
the likely instability of measurements at the upper range and the
absence of data from the proposed two-tier approach.
As indicated in their letter, CASAC concluded that the potential
instability in higher percentile NO2 concentrations near
major roads argues for a 98th, rather than a 99th, percentile form.
Several State organizations and agencies (e.g., NESCAUM and agencies in
IN, NC, SD, VA) and industry groups (e.g., AAM, ACC, API, AirQuality
Research and Logistics (AQRL), CPA, Dow, ExxonMobil, IPAMS, PAW, UPA)
also recommended a 98th percentile form in order to provide regulatory
stability. In contrast, a small number of State and local agencies
(e.g., in MO and TX), several environmental organizations (e.g., EDF,
EJ, GASP, NRDC), and medical/public health organizations (e.g., ALA,
ATS) recommended either a 99th percentile form or a more stringent form
(e.g., no exceedance) to further limit the occurrence of NO2
concentrations that exceed the standard level in locations that attain
the standard.
c. Conclusions On Form
The Administrator recognizes that there is not a clear health basis
for selecting one specific form over another. She also recognizes that
the analyses of different forms in the REA are most directly relevant
to a standard that reflects NO2 concentrations permitted to
occur broadly across a community, rather than the maximum concentration
that can occur anywhere in the area. In contrast, as discussed below
(section II.F.4.c), the Administrator has judged it appropriate to set
a new 1-hour standard that reflects the maximum allowable
NO2 concentration anywhere in an area. In light of this, the
Administrator places particular emphasis on the comments received on
form from CASAC relating to a 1-hour standard level that reflects the
maximum allowable NO2 concentration anywhere in an area. In
particular, the Administrator notes that CASAC recommended a 98th
percentile form averaged over 3 years for such a standard, given the
potential for instability in the higher percentile concentrations
around major roadways.
In considering this recommendation, the Administrator recognizes
that the public health protection provided by the 1-hour NO2
standard is based on the approach used to set the standard and the
level of the standard (see below), in conjunction with the form of the
standard. Given that the Administrator is setting a standard that
reflects the maximum allowable NO2 concentration anywhere in
an area, rather than a standard that reflects the allowable area-wide
NO2 concentration, she agrees with CASAC that an appropriate
consideration with regard to form is the extent to which specific
statistics could be unstable at locations where maximum NO2
concentrations are expected, such as near major roads. When considering
alternative forms for the standard, the Administrator notes that an
unstable form could result in areas shifting in and out of attainment,
potentially disrupting ongoing air quality planning without achieving
public health goals. Given the limited available information on the
variability in peak NO2 concentrations near important
sources of NO2 such as major roadways, and given the
recommendation from CASAC that the potential for instability in the
99th percentile concentration is cause for supporting a 98th percentile
form, the Administrator judges it appropriate to set the form based on
the 3-year average of the 98th percentile of the annual distribution of
1-hour daily maximum NO2 concentrations.
4. Level
As discussed below and in more detail in the proposal (section
II.F.4), the Administrator has considered two different approaches to
setting the 1-hour NO2 primary NAAQS. In the proposal, each
of these approaches was linked with a different range of standard
levels. Specifically, the Administrator proposed to set a 1-hour
standard reflecting the maximum allowable NO2 concentration
anywhere in an area and to set the level of such a standard from 80 to
100 ppb. The Administrator also solicited comment on the alternative
approach of setting a standard that reflects the allowable area-wide
NO2 concentration and setting the standard level from 50 to
75 ppb. This section summarizes the rationale for the Administrator's
proposed approach and range of standard levels (II.F.3.a), describes
the alternative approach and range of standard levels (II.F.3.b),
discusses comments related to each approach and range of standard
levels (II.F.3.c), and presents the Administrator's final conclusions
regarding the approach and level (II.F.3.d).
a. Rationale For Proposed Decisions on Approach and Level
In assessing the most appropriate approach to setting the 1-hour
standard and the most appropriate range of standard levels to propose,
the Administrator considered the broad body of scientific evidence
assessed in the ISA, including epidemiologic and controlled human
exposure studies, as well as the results of exposure/risk analyses
presented in the REA. In light of the body of available evidence and
analyses, as described above, the Administrator concluded in the
proposal that it is necessary to provide increased public health
protection for at-risk individuals against an array of adverse
respiratory health effects linked with short-term (i.e., 30 minutes to
24 hours) exposures to NO2. Such health effects have been
associated with exposure to the distribution of short-term ambient
NO2 concentrations across an area, including higher short-
term (i.e., peak) exposure concentrations, such as those that can occur
on or near major roadways and near other sources of NO2, as
well as the lower short-term exposure concentrations that can occur in
areas not near major roadways or other sources of NO2. The
Administrator's proposed decisions on approach and level, as discussed
in detail in the proposal (section II.F.4), are outlined below.
In considering a standard-setting approach, the Administrator was
mindful in the proposal that the available evidence and analyses from
the ISA and REA support the public health importance of roadway-
associated NO2 exposures. The exposure assessment described
in the REA estimated that roadway-associated exposures account for the
majority of exposures to peak NO2 concentrations (REA,
Figures 8-17, 8-18). The ISA concluded (section 4.3.6) that
NO2 concentrations in heavy traffic or on freeways ``can be
twice the residential outdoor or residential/arterial road level.'' In
considering the potential variability in the NO2
concentration gradient, the proposal noted that available monitoring
studies suggest that NO2 concentrations could be 30 to 100%
higher than those in the same area but away from the road.\12\
---------------------------------------------------------------------------
\12\ In addition, the air quality analyses presented in the REA
estimated that on-road NO2 concentrations are about 80%
higher on average than concentrations away from the road (REA,
section 7.3.2) and that NO2 monitors within 20 m of roads
measure NO2 concentrations that are, on average across
locations, 40% higher than concentrations measured by monitors at
least 100 m from the road (REA, compare Tables 7-11 and 7-13).
---------------------------------------------------------------------------
[[Page 6494]]
The Administrator also considered that millions of people in the
United States live, work, and/or attend school near important sources
of NO2 such as major roadways (ISA, section 4.4), and that
ambient NO2 concentrations in these locations vary depending
on the distance from major roads (i.e., the closer to a major road, the
higher the NO2 concentration) (ISA, section 2.5.4).
Therefore, these populations, which likely include a disproportionate
number of individuals in groups with higher prevalence of asthma and
higher hospitalization rates for asthma (e.g. ethnic or racial
minorities and individuals of low socioeconomic status) (ISA, section
4.4), are likely exposed to NO2 concentrations that are
higher than those occurring away from major roadways.
Given the above considerations, the Administrator proposed an
approach to setting the 1-hour NO2 primary NAAQS whereby the
standard would reflect the maximum allowable NO2
concentration anywhere in an area. In many locations, this
concentration is likely to occur on or near a major roadway. EPA
proposed to set the level of the standard such that, when available
information regarding the concentration gradient around roads is
considered, appropriate public health protection would be provided by
limiting the higher short-term peak exposure concentrations expected to
occur on and near major roadways, as well as the lower short-term
exposure concentrations expected to occur away from those roadways. The
Administrator concluded that this approach to setting the 1-hour
NO2 NAAQS would be expected to protect public health against
exposure to the distribution of short-term NO2
concentrations across an area and would provide a relatively high
degree of confidence regarding the protection provided against peak
exposures to higher NO2 concentrations, such as those that
can occur around major roadways. The remainder of this section
discusses the proposed range of standard levels.
In considering the appropriate range of levels to propose for a
standard that reflects the maximum allowable NO2
concentration anywhere in an area, the Administrator considered the
broad body of scientific evidence and exposure/risk information as well
as available information on the relationship between NO2
concentrations near roads and those away from roads. Specifically, she
considered the extent to which a variety of levels would be expected to
protect at-risk individuals against increased airway responsiveness,
respiratory symptoms, and respiratory-related emergency department
visits and hospital admissions.
After considering the scientific evidence and the exposure/risk
information (see sections II.B, II.C, and II.F.4.a.1 through II.F.4.a.3
in the proposal), as well as the available information on the
NO2 concentration gradient around roadways (section II.A.2
above and in the proposal), the Administrator concluded that the
strongest support is for a standard level at or somewhat below 100 ppb.
The Administrator's rationale in reaching this proposed conclusion is
provided below.
The Administrator noted that a standard level at or somewhat below
100 ppb in conjunction with the proposed approach would be expected to
limit short-term NO2 exposures to concentrations that have
been reported to increase airway responsiveness in asthmatics (i.e., at
or above 100 ppb). While she acknowledged that exposure to
NO2 concentrations below 100 ppb could potentially increase
airway responsiveness in some asthmatics, the Administrator also noted
uncertainties regarding the magnitude and the clinical significance of
the NO2-induced increase in airway responsiveness, as
discussed in the policy assessment chapter of the REA (section
10.3.2.1, discussed in section II.F.4.e in the proposal). Given these
uncertainties, the Administrator concluded in the proposal that
controlled human exposure studies provide support for limiting
exposures at or somewhat below 100 ppb NO2.
The Administrator also noted that a standard level at or somewhat
below 100 ppb in conjunction with the proposed approach would be
expected to maintain peak area-wide NO2 concentrations
considerably below those measured in locations where key U.S.
epidemiologic studies have reported associations with more serious
respiratory effects, as indicated by increased emergency department
visits and hospital admissions. Specifically, the Administrator noted
that 5 key U.S. studies provide evidence for such associations in
locations where the 99th percentile of the distribution of 1-hour daily
maximum NO2 concentrations measured at area-wide monitors
ranged from 93 to 112 ppb (Ito et al., 2007; Jaffe et al., 2003; Peel
et al., 2005; Tolbert et al., 2007; and a study by the New York State
Department of Health, 2006).\13\ The Administrator concluded that these
studies provide support for a 1-hour standard that limits the 99th
percentile of the distribution of 1-hour daily maximum area-wide
NO2 concentrations to below 90 ppb (corresponds to a 98th
percentile concentration of 85 ppb), and that limiting area-wide
concentrations to considerably below 90 ppb would be appropriate in
order to provide an adequate margin of safety. The Administrator noted
that, based on available information about the NO2
concentration gradient around roads, a standard level at or somewhat
below 100 ppb set in conjunction with the proposed approach would be
expected to accomplish this. Specifically, she noted that given
available information regarding NO2 concentration gradients
around roads (see section II.A.2), a standard level at or below 100 ppb
(with either a 99th or 98th percentile form) would be expected to limit
peak area-wide NO2 concentrations to approximately 75 ppb or
below.\14\ Therefore, the Administrator concluded that a standard level
at or somewhat below 100 ppb under the proposed approach would be
expected to maintain peak area-wide NO2 concentrations well
below 90 ppb across locations despite the expected variation in the
NO2 concentration gradient that can exist around roadways in
different locations and over time.
---------------------------------------------------------------------------
\13\ The 98th percentile concentrations in these study locations
ranged from 85 to 94 ppb.
\14\ For a standard of 100 ppb, area-wide concentrations would
be expected to range from approximately 50 ppb (assuming near-road
concentrations are 100% higher than area-wide concentrations) to 75
ppb (assuming near-road concentrations are 30% higher than area-wide
concentrations).
---------------------------------------------------------------------------
The Administrator also noted that a study by Delfino provides mixed
evidence for effects in a location with area-wide 98th and 99th
percentile 1-hour daily maximum NO2 concentrations of 50 and
53 ppb, respectively. In that study, NO2 effect estimates
were positive, but some reported 95% confidence limits for the odds
ratio (OR) that included values less than 1.00. Given the mixed results
of the Delfino study, the Administrator concluded that it may not be
necessary to maintain area-wide NO2 concentrations at or
below 50 ppb to provide protection against the effects reported in
epidemiologic studies.
In addition to these evidence-based considerations, the
Administrator noted that a standard level at or somewhat below 100 ppb
under the proposed approach would be consistent with the
[[Page 6495]]
results of the exposure and risk analyses presented in the REA. As
discussed in section II.C of the proposal, the results of these
analyses provide support for setting a standard that limits 1-hour
area-wide NO2 concentrations to between 50 and 100 ppb. As
described above, a standard level of 100 ppb that reflects the maximum
allowable NO2 concentration would be expected to maintain
area-wide NO2 concentrations at or below approximately 75
ppb. Given all of these considerations, the Administrator concluded in
the proposal that a standard level at or somewhat below 100 ppb (with a
99th percentile form), in conjunction with the proposed approach, would
be requisite to protect public health with an adequate margin of safety
against the array of NO2-associated health effects.
In addition to the considerations discussed above, which support
setting a standard level at or somewhat below 100 ppb, the
Administrator also considered the extent to which available evidence
could support standard levels below 100 ppb. The Administrator
concluded that the evidence could support setting the standard level
below 100 ppb to the extent the following were emphasized:
The possibility that an NO2-induced increase in
airway responsiveness could occur in asthmatics following exposures to
concentrations below 100 ppb and/or the possibility that such an
increase could be clinically significant.
The mixed results reported in the study by Delfino et al.
(2002) of an association between respiratory symptoms and the
relatively low ambient NO2 concentrations measured in the
study area.
Specifically, she noted that a standard level of 80 ppb (99th
percentile form), in conjunction with the proposed approach, could
limit area-wide NO2 concentrations to 50 ppb \15\ and would
be expected to limit exposure concentrations to below those that have
been reported to increase airway responsiveness in asthmatics. For the
reasons stated above, the Administrator proposed to set the level of a
new 1-hour standard between 80 ppb and 100 ppb.
---------------------------------------------------------------------------
\15\ This conclusion assumes that near-road NO2
concentrations are 65% higher than area-wide concentrations,
reflecting the mid-point in the range of 30 to 100%. Based on
available information suggesting that near-road concentrations can
be 30 to 100% higher than area-wide concentrations, a standard level
of 80 ppb could limit area-wide concentrations to between 40 and 60
ppb.
---------------------------------------------------------------------------
b. Rationale for the Alternative Approach and Range of Levels
As described above, the Administrator proposed to set a 1-hour
NO2 NAAQS reflecting the maximum allowable NO2
concentration anywhere in an area and to set the level of such a
standard from 80 to 100 ppb. However, prior to the proposal, the
approach of setting a 1-hour NO2 NAAQS that reflects the
maximum allowable NO2 concentration anywhere in an area had
not been discussed by EPA in the REA or considered by CASAC. Rather,
the potential alternative standards discussed in the REA, and reviewed
by CASAC, reflected allowable area-wide NO2 concentrations
(i.e., concentrations that occur broadly across communities).
Given this, the Administrator noted in the proposal that comments
received on the approach to setting the 1-hour standard (i.e., from
CASAC and from members of the public) could provide important new
information for consideration. Therefore, the Administrator also
solicited comment on the alternative approach of setting a 1-hour
NO2 primary NAAQS that would reflect the allowable area-wide
NO2 concentration, analogous to the standards evaluated in
the REA, and with a level set within the range of 50 to 75 ppb. In
discussing this alternative approach with a standard level from 50 to
75 ppb, the Administrator noted the following in the proposal:
Such a standard would be expected to maintain area-wide
NO2 concentrations below peak 1-hour area-wide
concentrations measured in locations where key U.S. epidemiologic
studies have reported associations with respiratory-related emergency
department visits and hospital admissions.
Standard levels from the lower end of the range would be
expected to limit roadway-associated exposures to NO2
concentrations that have been reported in controlled human exposure
studies to increase airway responsiveness in asthmatics. Specifically,
a standard level of 50 ppb under this approach could limit near-road
concentrations to between approximately 65 and 100 ppb, depending on
the relationship between near-road NO2 concentrations and
area-wide concentrations.
This alternative approach would provide relatively more
confidence regarding the degree to which a specific standard level
would limit area-wide NO2 concentrations and less confidence
regarding the degree to which a specific standard level would limit the
peak NO2 concentrations likely to occur near major roadways.
c. Comments on Approach and Level
In the proposal, each approach to setting the 1-hour standard, and
each range of standard levels, was linked to different requirements for
the design of the NO2 monitoring network. Specifically, in
conjunction with the proposed approach (i.e., standard reflects the
maximum allowable NO2 concentration anywhere in an area and
the level is set within the range of 80 to 100 ppb), the Administrator
proposed to establish a 2-tiered monitoring network that would include
monitors sited to measure the maximum NO2 concentrations
anywhere in an area, including near major roadways, and monitors sited
to measure maximum area-wide NO2 concentrations. In
conjunction with the alternative approach (i.e., standard reflects the
allowable area-wide NO2 concentration and the level is set
within the range of 50 to 75 ppb), the Administrator solicited comment
on a monitoring network that would only include area-wide
NO2 monitors. Because of these linkages in the proposal,
most commenters combined their comments on the approach to setting a 1-
hour standard and on the standard level with their comments on the
monitoring requirements. In this section, we discuss comments from
CASAC and public commenters on the approach to setting a 1-hour
standard and on the standard level. Comments on the monitoring network
are also discussed in this section to the extent they indicate a
preference for either the proposed or alternative approach to setting
the 1-hour standard. More specific comments on monitor placement and
network design are discussed below in section III.B.2 and in the
Response to Comments document. EPA responses to technical comments on
the scientific evidence and the exposure/response information are
discussed above in section II.E.2 and in the Response to Comments
document. The Administrator's response to commenters' views on the
approach to setting the 1-hour standard and on the standard level is
embodied in the discussed in section II.F.4.d.
i. CASAC Comments on the Approach to Setting the Standard
A majority of CASAC and CASAC Panel members \16\ favored the
proposed approach of setting a 1-hour standard that reflects the
maximum allowable
[[Page 6496]]
NO2 concentration anywhere in an area and linking such a
standard with a 2-tiered monitoring network that would include both
near-road and area-wide monitors, though CASAC did not reach consensus
on this approach. Specifically, in their letter to the Administrator
(Samet, 2009), CASAC stated the following:
---------------------------------------------------------------------------
\16\ CASAC members were also part of the CASAC Panel for the
NO2 NAAQS review (i.e., the Oxides of Nitrogen Primary
National Ambient Air Quality Standards Panel). Therefore, references
to the CASAC Panel include both CASAC members and Panel members.
There was a split view on the two approaches among both CASAC
and CASAC panel members with a majority of each favoring the
Agency's proposed two-tiered monitoring network because they thought
this approach would be more effective in limiting near-roadway
exposures that may reach levels in the range at which some
individuals with asthma may be adversely affected. Other members
acknowledged the need for research and development of near-road
monitoring data for criteria pollutants in general but favored
retention of EPA's current area-wide monitoring for NO2
regulatory purposes, due to the lack of epidemiological data based
on near-roadway exposure measurements and issues related to
---------------------------------------------------------------------------
implementing a near-road monitoring system for NO2.
Thus, the recommendation of the majority of CASAC Panel members was
based on their conclusion that the proposed approach would be more
effective than the alternative at limiting near-roadway exposures to
NO2 concentrations that could adversely affect asthmatics.
In addition, these CASAC Panel members noted important uncertainties
with the alternative approach. Specifically, they stated the following
(Samet, 2009):
Panel members also supported the proposed two-tiered approach
because basing regulations on area-wide monitoring alone was
problematic. Such an approach would require EPA to embed
uncertainties and assumptions about the relationship between area-
wide and road-side monitoring into the area-wide standard.
A minority of CASAC Panel members expressed support for the
alternative approach of setting a 1-hour standard that reflects the
allowable area-wide NO2 concentration. These CASAC Panel
members concluded that there would be important uncertainties
associated with the proposed approach. Specifically, they noted that
the key U.S. NO2 epidemiologic studies relied upon area-wide
NO2 concentrations. In their view, the use of area-wide
concentrations in these studies introduces uncertainty into the
selection of a standard level for a standard that reflects the maximum
allowable NO2 concentration anywhere in an area and that is
linked with a requirement to place monitors near major roads. As a
result of this uncertainty, CASAC Panel members who favored the
alternative approach noted that ``it would be better to set the
standard on the same area-wide monitoring basis as employed in the
epidemiologic studies upon which it [the standard] now relies'' (Samet,
2009). These CASAC Panel members also strongly supported obtaining
monitoring data near major roads, while recognizing uncertainties
associated with identifying appropriate monitoring sites near roads
(see section III.B.2 and the Response to Comments document for more
discussion of CASAC's monitoring comments).
ii. Public Comments on the Approach to Setting the Standard
Consistent with the views expressed by the majority of CASAC
members, a number of commenters concluded that the most appropriate
approach would be to set a 1-hour standard that reflects the maximum
allowable NO2 concentration anywhere in an area and to
couple that standard with a requirement that monitors be placed in
locations where maximum concentrations are expected, including near
major roads. This view was expressed by some State and local agencies
(e.g., in CA, IA, NY, TX, WA, WI), by a number of environmental
organizations (e.g., CAC, EDF, EJ, GASP, NRDC), by the ALA, and
individual commenters. Several additional medical and public health
organizations (ACCP, AMA, ATS, NADRC, NACPR) did not explicitly express
a recommendation regarding the approach though these organizations did
recommend that, in setting a 1-hour standard, particular attention
should be paid to NOX concentrations around major roadways.
In support of their recommendation to adopt the proposed approach and
to focus monitoring around major roads, these commenters generally
concluded that a primary consideration should be the extent to which
the NO2 NAAQS protects at-risk populations that live and/or
attend school near important sources of NO2 such as major
roads. As such, these comments supported the rationale in the proposal
for setting a 1-hour standard that reflects the maximum allowable
NO2 concentration anywhere in an area.
A number of State commenters expressed the view that area-wide
monitors should be used for attainment/non-attainment determinations
(e.g., NACAA, NESCAUM and agencies in IL, IN, MI, MS, NC, NM, SC). One
State commenter (NESCAUM) agreed with EPA concerns about near-road
exposures but concluded that it is premature to establish a large near-
road monitoring network at this time due to uncertainty regarding the
relationship between near-road and area-wide NO2
concentrations and the variability in that relationship. NESCAUM
recommended that EPA work with States to establish a targeted
monitoring program in select urban areas to gather data that would
inform future modifications to the monitoring network, but that ``[t]he
existing area-wide monitoring network should be used to identify
initial nonattainment areas.'' Other State commenters also concluded
that the most appropriate approach would be to base non-attainment
determinations only on area-wide monitors. Based on their monitoring
comments, many of these commenters appeared to support setting a 1-hour
standard that reflects the allowable area-wide NO2
concentration. State concerns with the proposed approach often included
uncertainties associated with identifying and accessing appropriate
monitor sites near major roads, as well as concerns related to
implementation and cost to States (as discussed further in the Response
to Comments document, the Administrator may not consider cost of
implementation in decisions on a NAAQS).
One commenter (AAM) concluded that the focus of the proposed
approach on NO2 concentrations around major roadways is not
justified because the REA and the proposal overstate the extent to
which NO2 concentrations near roads are higher than
NO2 concentrations farther away from the road. This
conclusion is based on an analysis of 42 existing NO2
monitors in 6 locations. Comparing NO2 concentrations
measured by these monitors, some of which are closer to roads and
others of which are farther from roads, AAM concluded that ``roadside
monitors are not measuring high NO2 concentrations.''
We agree that there is uncertainty associated with estimates of
roadway-associated NO2 concentrations (see REA, sections
7.4.6 and 8.4.8.3 for detailed discussion of these uncertainties) and
in identifying locations where maximum concentrations are expected to
occur. However, we note that the Administrator's conclusions regarding
the relationship between NO2 concentrations near roads and
those away from roads rely on multiple lines of scientific evidence and
information. Specifically, the Administrator relied in the proposal on
the following in drawing conclusions regarding the distribution of
NO2 concentrations across areas:
Monitoring studies discussed in the ISA and REA that were
designed to characterize the NO2 concentration gradient
around roads, which indicated that NO2 concentrations near
roads can
[[Page 6497]]
be approximately 30 to 100% higher than concentrations away from the
road in the same area.
Air quality and exposure analyses presented in the REA
which estimate that, on average across locations, NO2
concentrations on roads could be 80% higher than those away from roads
and that roadway-associated exposures account for the majority of
exposures to NO2 concentrations at or above 100 ppb.
In contrast, the existing NO2 monitoring network, which
was the basis for the analysis submitted by AAM, was not designed to
characterize the spatial gradients in NO2 concentrations
surrounding roadways. Rather, concentrations of NO2 measured
by existing monitors are likely to reflect contributions from a
combination of mobile and stationary sources, with one or the other
dominating depending on the proximity of these sources to the monitors.
Therefore, we conclude that the analysis submitted by AAM, which does
not consider other relevant lines of evidence and information, does not
appropriately characterize the relationship between NO2
concentrations near roads and those away from roads. (See the Response
to Comments document for a more detailed discussion of AAM comments.)
In addition, we note that, although the Administrator concluded in
the proposal that maximum NO2 concentrations in many areas
are likely to occur around major roads, she also recognized that
maximum concentrations can occur elsewhere in an area. For this reason,
she proposed to set a 1-hour NO2 standard that reflects the
maximum allowable NO2 concentration anywhere in an area,
regardless of where that maximum concentration occurs.\17\ Therefore,
the proposed approach to setting the standard would be expected to
limit the maximum NO2 concentrations anywhere in an area
even if in some areas, as is contended by AAM, those maximum
NO2 concentrations do not occur near roads.
---------------------------------------------------------------------------
\17\ To measure maximum concentrations, the Administrator
proposed monitoring provisions that would require monitors within 50
meters of major roads and to allow the Regional Administrator to
require additional monitors in situations where maximum
concentrations would be expected to occur in locations other than
near major roads (e.g., due to the influence of multiple smaller
roads and/or stationary sources).
---------------------------------------------------------------------------
iii. CASAC Comments on Standard Level
In commenting on the proposal, CASAC discussed both the proposed
range of standard levels (i.e., 80-100 ppb) and the alternative range
of standard levels (i.e., 50-75 ppb). CASAC did express the consensus
conclusion that if the Agency finalizes a 1-hour standard in accordance
with the proposed approach (i.e., standard level reflects the maximum
allowable NO2 concentration anywhere in an area), then it is
appropriate to consider the proposed range of standard levels from 80
to 100 ppb. Specifically, the CASAC letter to the Administrator on the
proposal (Samet, 2009) stated the following with regard to the proposed
approach:
[T]he level of the one-hour NO2 standard should be
within the range of 80-100 ppb and not above 100 ppb. In its letter
of December 2, 2008, CASAC strongly voiced a consensus view that the
upper end of the range should not exceed 100 ppb, based on evidence
of risk at that concentration. The lower limit of 80 ppb was viewed
as reasonable by CASAC; selection of a value lower than 80 ppb would
represent a policy judgment based on uncertainty and the degree of
public health protection sought, given the limited health-based
evidence at concentrations below 100 ppb.
CASAC also recommended that this level be employed with a 98th
percentile form, in order to promote the stability of the standard (see
above for discussion of form).
iv. Public Comments on Standard Level
A number of State and local agencies and organizations expressed
support for setting the level of the 1-hour NO2 standard
within the proposed range of 80 to 100 ppb. While some State and local
agencies (e.g., in CA, IA, MI, NY, TX) made this recommendation in
conjunction with a recommendation to focus monitoring near major roads
and other important sources of NO2, a number of State
commenters (e.g., NACAA, NESCAUM and agencies in IL, NC, NM, TX, VA)
recommended a standard level from 80 to 100 ppb in conjunction with a
recommendation that only area-wide monitors be deployed for purposes of
determining attainment with the standard. Based on these monitoring
comments, these State commenters appear to favor an approach where a
standard level from 80 to 100 ppb would reflect the allowable area-wide
NO2 concentration. As discussed above (and in more detail in
section III.B.2 and the Response to Comments document), State
commenters often based these recommendations on uncertainties
associated with designing an appropriate national near-road monitoring
network.
A number of environmental organizations (e.g., CAC, EDF, EJ, GASP,
NRDC) and medical/public health organizations (e.g., ACCP, ALA, AMA,
ATS, NACPR, NAMDRC) supported setting a standard level below 80 ppb for
a standard that reflects the maximum allowable NO2
concentration anywhere in an area. Several of these groups recommended
a standard level of 50 ppb. This recommendation was typically based on
the commenters' interpretation of the epidemiologic and controlled
human exposure evidence, as described below.
Some of these commenters noted that the 98th percentile area-wide
NO2 concentration was below 80 ppb in the location of a
single key U.S. epidemiologic study (i.e., 50 ppb in study by Delfino).
Given this, commenters concluded that the standard level should be set
at 50 ppb. Their comments on the monitoring network generally favored a
requirement to place monitors near major roads and, therefore, these
commenters appeared to favor a standard level as low as 50 ppb and to
recommend that such a standard level reflect the maximum allowable
NO2 concentration anywhere in an area. In their comments,
the ALA, EDF, EJ, and NRDC stated the following:
Considering the Delfino study alone on EPA's terms, that is,
focusing on the 98th percentile of the 1-hour daily maximum
concentrations, EPA reports a concentration of 50 ppb where asthma
symptoms were observed. Based primarily on this study, EPA concluded
in the REA that it was appropriate to set the lower end of the range
at 50 ppb, which corresponded to the lowest-observed effects level
of airway hyperresponsiveness in asthmatics. To provide the
strongest public health protection, we therefore urge the level of
the standard be set at 50 ppb.
In some cases, the same commenters also appeared to recommend setting a
standard level below 50 ppb because mean area-wide NO2
concentrations reported in locations of key U.S. epidemiologic studies
are below this concentration. Specifically, with regard to the key U.S.
epidemiologic studies, these commenters (e.g., ALA, EDF, EJ, NRDC)
stated the following:
These studies clearly identify adverse health effects such as
emergency room visits and hospital admissions for respiratory causes
at concentrations currently occurring in the United States. Mean
concentrations for all but two of these studies are about or below
50 ppb, suggesting that the standard must be set below this level to
allow for a margin of safety.
The Administrator's consideration of the Delfino study as it relates to
a decision on standard level is discussed below (section II.F.4.d).
Regarding the recommendation to set the level below 50 ppb based on
mean area-wide NO2 concentrations in epidemiologic study
[[Page 6498]]
locations, we note that the Administrator proposed to set a standard
that reflects the maximum allowable NO2 concentration
anywhere in an area and to set the form of that standard at the upper
end of the distribution of 1-hour daily maximum NO2
concentrations.\18\ As described in the proposal, such a standard, with
a level from the proposed range of 80 to 100 ppb, would be expected to
maintain peak area-wide NO2 concentrations below the peak
area-wide concentrations measured in locations where key U.S.
epidemiologic studies have reported associations with respiratory-
related emergency department visits and hospital admissions. Because
reducing NOX emissions to meet a 98th percentile
NO2 standard should lower the distribution of NO2
concentrations, including the mean, a standard that limits the 98th
percentile of the distribution of 1-hour daily maximum concentrations
would also be expected to limit mean concentrations. Therefore,
although we acknowledge that the relationship between peak and mean
NO2 concentrations will likely vary across locations and
over time, if peak area-wide NO2 concentrations are
maintained below those in key epidemiologic study locations, mean area-
wide NO2 concentrations would also be expected to be
maintained below the mean area-wide concentrations in those locations
(see ISA, figure 2.4-13 for information on the relationship between
peak and mean NO2 concentrations).
---------------------------------------------------------------------------
\18\ As discussed above, the Administrator has selected the 98th
percentile as the form for the new 1-hour NO2 standard.
---------------------------------------------------------------------------
As discussed above (section, II.E.2), a number of industry groups
did not support setting a new 1-hour NO2 standard. However,
several of these groups (e.g., AAM, Dow, NAM, NPRA) also concluded
that, if EPA does choose to set a new 1-hour standard, the level of
that standard should be above 100 ppb. As a basis for this
recommendation, these groups emphasized uncertainties in the scientific
evidence. Specifically, as discussed in more detail above (section
II.E.2), these commenters typically concluded that available
epidemiologic studies do not support the conclusion that NO2
causes reported health effects. This was based on their assertion that
the presence of co-pollutants in the ambient air precludes the
identification of a specific NO2 contribution to reported
effects. As a result, these commenters recommended that a 1-hour
standard should be based on the controlled human exposure evidence and
that, in considering that evidence, EPA should rely on the meta-
analysis of NO2 airway responsiveness studies conducted by
Goodman et al., (2009) rather than the meta-analysis included in the
final ISA. As described above, they concluded that in relying on the
ISA meta-analysis, EPA has inappropriately relied on a new unpublished
meta-analysis that has not been peer-reviewed, was not reviewed by
CASAC, and was not conducted in a transparent manner. EPA recognizes
the uncertainties in the scientific evidence that are discussed by
these industry commenters; however, we strongly disagree with their
conclusions regarding the implications of these uncertainties for
decisions on the NO2 NAAQS. These comments, and EPA's
responses, are discussed in detail above (section II.E.2) and in the
Response to Comments document and are summarized briefly below.
As noted in section II.E.2, we agree that the presence of co-
pollutants in the ambient air complicates the interpretation of
epidemiologic studies; however, our conclusions regarding causality are
based on consideration of the broad body of epidemiologic studies
(including those employing multi-pollutant models) as well as animal
toxicological and controlled human exposure studies. The ISA concluded
that this body of evidence ``supports a direct effect of short-term
NO2 exposure on respiratory morbidity at ambient
concentrations below the current NAAQS level'' (ISA, p. 5-16). In
addition, the ISA (p. 5-15) concluded the following:
[T]he strongest evidence for an association between
NO2 exposure and adverse human health effects comes from
epidemiologic studies of respiratory symptoms and ED visits and
hospital admissions. These new findings were based on numerous
studies, including panel and field studies, multipollutant studies
that control for the effects of other pollutants, and studies
conducted in areas where the whole distribution of ambient 24-h avg
NO2 concentrations was below the current NAAQS level of
0.053 ppm (53 ppb) (annual average).
Given that epidemiologic studies provide the strongest support for an
association between NO2 and respiratory morbidity, and that
a number of these studies controlled for the presence of other
pollutants with multi-pollutant models (in which NO2 effect
estimates remained robust), we disagree that NO2
epidemiologic studies should not be used to inform a decision on the
level of the 1-hour NO2 standard.
In addition, we agree that uncertainty exists regarding the extent
to which the NO2-induced increase in airway responsiveness
is adverse (REA, section 10.3.2.1); however, as discussed in detail
above (section II.E.2), we disagree with the conclusion by many
industry commenters that this effect is not adverse in asthmatics
following exposures from 100 to 600 ppb NO2. Specifically,
we do not agree that the approach taken in the study by Goodman et al.
(2009), which was used by many industry commenters to support their
conclusions, was appropriate. The authors of the Goodman study used
data from existing NO2 studies to characterize the dose-
response relationship of NO2 and airway responsiveness and
to calculate the magnitude of the NO2 effect. Given the
protocol differences in existing studies of NO2 and airway
responsiveness, we do not agree that it is appropriate to base such an
analysis on these studies.
The Administrator's consideration of these uncertainties, within
the context of setting a standard level, is discussed in the next
section.
d. Conclusions on Approach and Standard Level
Having carefully considered the public comments on the appropriate
approach and level for a 1-hour NO2 standard, as discussed
above, the Administrator believes the fundamental conclusions reached
in the ISA and REA remain valid. In considering the approach, the
Administrator continues to place primary emphasis on the conclusions of
the ISA and the analyses of the REA, both of which focus attention on
the importance of roadways in contributing to peak NO2
exposures, given that roadway-associated exposures can dominate
personal exposures to NO2. In considering the level at which
the 1-hour primary NO2 standard should be set, the
Administrator continues to place primary emphasis on the body of
scientific evidence assessed in the ISA, as summarized above in section
II.B, while viewing the results of exposure and risk analyses,
discussed above in section II.C, as providing information in support of
her decision.
With regard to her decision on the approach to setting the 1-hour
standard, the Administrator continues to judge it appropriate to
provide increased public health protection for at-risk individuals
against an array of adverse respiratory health effects linked with
short-term exposures to NO2, where such health effects have
been associated with exposure to the distribution of short-term ambient
NO2 concentrations across
[[Page 6499]]
an area. In protecting public health against exposure to the
distribution of short-term NO2 concentrations across an
area, the Administrator is placing emphasis on providing a relatively
high degree of confidence regarding the protection provided against
exposures to peak concentrations of NO2, such as those that
can occur around major roadways. Available evidence and information
suggest that roadways account for the majority of exposures to peak
NO2 concentrations and, therefore, are important
contributors to NO2-associated public health risks. In
reaching this conclusion, the Administrator notes the following:
Mobile sources account for the majority of NOX
emissions (ISA, Table 2.2-1).
The ISA stated that NO2 concentrations in heavy
traffic or on freeways ``can be twice the residential outdoor or
residential/arterial road level,'' that ``exposure in traffic can
dominate personal exposure to NO2,'' and that
``NO2 levels are strongly associated with distance from
major roads (i.e., the closer to a major road, the higher the
NO2 concentration)'' (ISA, sections 2.5.4, 4.3.6).
The exposure assessment presented in the REA estimated
that roadway-associated exposures account for the majority of exposures
to peak NO2 concentrations (REA, Figures 8-17, 8-18).
Monitoring studies suggest that NO2
concentrations near roads can be considerably higher than those in the
same area but away from roads (e.g., by 30-100%, see section II.A.2).
In their comments on the approach to setting the 1-hour
NO2 standard, the majority of CASAC Panel members emphasized
the importance of setting a standard that limits roadway-associated
exposures to NO2 concentrations that could adversely affect
asthmatics. These CASAC Panel members favored the proposed approach,
including its focus on roads.
In addition, the Administrator notes that a considerable fraction
of the population resides, works, or attends school near major roadways
or other sources of NO2 and that these populations are
likely to have increased exposure to NO2 (ISA, section 4.4).
Based on data from the 2003 American Housing Survey, approximately 36
million individuals live within 300 feet (~90 meters) of a four-lane
highway, railroad, or airport (ISA, section 4.4).\19\ Furthermore, in
California, 2.3% of schools with a total enrollment of more than
150,000 students were located within approximately 500 feet of high-
traffic roads (ISA, section 4.4). Of this population, which likely
includes a disproportionate number of individuals in groups with a
higher prevalence of asthma and higher hospitalization rates for asthma
(e.g., ethnic or racial minorities and individuals of low socioeconomic
status) (ISA, section 4.4), asthmatics and members of other susceptible
groups (e.g., children, elderly) will have the greatest risks of
experiencing health effects related to NO2 exposure. In the
United States, approximately 10% of adults and 13% of children have
been diagnosed with asthma, and 6% of adults have been diagnosed with
COPD (ISA, section 4.4).
---------------------------------------------------------------------------
\19\ The most current American Housing Survey (http://www.census.gov/hhes/www/housing/ahs/ahs.html) is from 2007 and lists
a higher fraction of housing units within the 300 foot boundary.
According to Table 1A-6 from that report (http://www.census.gov/hhes/www/housing/ahs/ahs07/tab1a-6.pdf), out of 128.2 million total
housing units in the United States, about 20 million were reported
by the surveyed occupant or landlord as being within 300 feet of a
4-or-more lane highway, railroad, or airport. That constitutes 15.6%
of the total housing units in the U.S. Assuming equal distributions,
with a current population of 306.3 million, that means that there
would be 47.8 million people meeting the 300 foot criteria.
---------------------------------------------------------------------------
In considering the approach to setting the 1-hour standard, the
Administrator also notes that concerns with the proposed approach
expressed by the minority of CASAC Panel members included concern with
the uncertainty in the relationship between near-road and area-wide
NO2 concentrations, given that U.S. epidemiologic studies
have been based on concentrations measured at area-wide monitors.
However, as discussed by the majority of CASAC Panel members, a similar
uncertainty would be involved in setting a standard with the
alternative approach (Samet, 2009). The Administrator agrees with the
majority of CASAC Panel members and concludes that uncertainty in the
relationship between near-road and area-wide NO2
concentrations should be considered regardless of the approach selected
to set the standard. She recognizes that this uncertainty can and
should be taken into consideration when considering the level of the
standard.
In drawing conclusions on the approach, the Administrator has
considered the extent to which each approach, in conjunction with the
ranges of standard levels discussed in the proposal, would be expected
to limit the distribution of NO2 concentrations across an
area and, therefore, would be expected to protect against risks
associated with NO2 exposures. Specifically, she has
considered the extent to which a standard set with each approach would
be expected to limit maximum NO2 concentrations and area-
wide NO2 concentrations.
With regard to expected maximum concentrations, the Administrator
notes the following:
A standard reflecting the maximum allowable NO2
concentration anywhere in an area would provide a relatively high
degree of confidence regarding the level of protection provided against
peak exposures, such as those that can occur on or near major roadways.
A standard level from anywhere within the proposed range (i.e., 80 to
100 ppb) would be expected to limit exposures to NO2
concentrations reported to increase airway responsiveness in
asthmatics.
A standard reflecting the allowable area-wide
NO2 concentration would not provide a high degree of
confidence regarding the extent to which maximum NO2
concentrations would be limited. Maximum NO2 concentrations
would be expected to be controlled to varying degrees across locations
and over time depending on the NO2 concentration gradient
around roads. Given the expected variability in gradients across
locations and over time, most standard levels within the range
considered in the proposal with this option (i.e., 50 to 75 ppb) would
not be expected to consistently limit the occurrence of NO2
concentrations that have been reported to increase airway
responsiveness in asthmatics.
With regard to expected area-wide concentrations, the Administrator
notes the following:
The extent to which a standard reflecting the maximum
allowable NO2 concentration anywhere in an area would be
expected to limit area-wide NO2 concentrations would vary
across locations, e.g., depending on the NO2 concentration
gradient around roads. However, in conjunction with a standard level
from anywhere within the proposed range (i.e., 80-100 ppb), such an
approach would be expected to maintain area-wide NO2
concentrations below those measured in locations where key U.S.
epidemiologic studies have reported associations between ambient
NO2 and respiratory-related hospital admissions and
emergency department visits (based on available information regarding
the NO2 concentration gradient around roads as discussed
below).
A standard reflecting the maximum allowable area-wide
NO2 concentration would provide a relatively high degree of
certainty regarding the extent to which area-wide NO2
concentrations are limited. In conjunction with a standard level from
anywhere within the range of
[[Page 6500]]
levels discussed in the proposal (i.e., 50-75 ppb) with this
alternative approach, such a standard would be expected to maintain
area-wide NO2 concentrations below those measured in
locations where key U.S. epidemiologic studies have reported
associations between ambient NO2 and respiratory-related
hospital admissions and emergency department visits.
Given the above considerations, the Administrator concludes that
both approaches, in conjunction with appropriate standard levels, would
be expected to maintain area-wide NO2 concentrations below
those measured in locations where key U.S. epidemiologic studies have
reported associations between ambient NO2 and respiratory-
related hospital admissions and emergency department visits. In
contrast, the Administrator concludes that only a standard reflecting
the maximum allowable NO2 concentration anywhere in an area,
in conjunction with an appropriate standard level, would be expected to
consistently limit exposures, across locations and over time, to
NO2 concentrations reported to increase airway
responsiveness in asthmatics. After considering the evidence and
uncertainties, and the advice of the CASAC Panel, the Administrator
judges that the most appropriate approach to setting a 1-hour standard
to protect against the distribution of short-term NO2
concentrations across an area, including the higher concentrations that
can occur around roads and result in elevated exposure concentrations,
is to set a standard that reflects the maximum allowable NO2
concentration anywhere in an area.
In considering the level of a 1-hour NO2 standard that
reflects the maximum allowable NO2 concentration anywhere in
an area, the Administrator notes that there is no bright line clearly
directing the choice of level. Rather, the choice of what is
appropriate is a public health policy judgment entrusted to the
Administrator. This judgment must include consideration of the
strengths and limitations of the evidence and the appropriate
inferences to be drawn from the evidence and the exposure and risk
assessments. Specifically, the Administrator notes the following:
Controlled human exposure studies have reported that
various NO2 exposure concentrations increased airway
responsiveness in mostly mild asthmatics (section II above and II.B.1.d
in proposal). These studies can inform an evaluation of the risks
associated with exposure to specific NO2 concentrations,
regardless of where those exposures occur in an area. Because
concentrations evaluated in controlled human exposure studies are at
the high end of the distribution of ambient NO2
concentrations (ISA, section 5.3.2.1), these studies most directly
inform consideration of the risks associated with exposure to peak
short-term NO2 concentrations.
Epidemiologic studies (section II.B.1.a and b) conducted
in the United States have reported associations between ambient
NO2 concentrations measured at area-wide monitors in the
current network and increased respiratory symptoms, emergency
department visits, and hospital admissions. Area-wide monitors in the
urban areas in which these epidemiologic studies were conducted are not
sited in locations where localized peak concentrations are likely to
occur. Thus, they do not measure the full range of ambient
NO2 concentrations across the area. Rather, the area-wide
NO2 concentrations measured by these monitors are used as
surrogates for the distribution of ambient NO2
concentrations across the area, a distribution that includes
NO2 concentrations both higher than (e.g., around major
roadways) and lower than the area-wide concentrations measured in study
locations. Epidemiologic studies evaluate whether area-wide
NO2 concentrations are associated with the risk of
respiratory morbidity. Available information on NO2
concentration gradients around roadways can inform estimates of the
relationship between the area-wide NO2 concentrations
measured in epidemiologic study locations and the higher NO2
concentrations likely to have occurred around roads in those locations,
which can then inform the decision on the level of a standard
reflecting the maximum allowable NO2 concentration anywhere
in an area.
The risk and exposure analyses presented in the REA
provide information on the potential public health implications of
setting standards that limit area-wide NO2 concentrations to
specific levels. While the Administrator acknowledges the uncertainties
associated with these analyses which, as discussed in the REA, could
result in either over- or underestimates of NO2-associated
health risks, she judges that these analyses are informative for
considering the relative levels of public health protection that could
be provided by different standards.
The Administrator's consideration of the controlled human exposure
evidence, epidemiologic evidence, and exposure/risk information are
discussed below specifically with regard to a decision on the level of
a standard that reflects the maximum allowable NO2
concentration anywhere in an area.
In considering the potential for controlled human exposure studies
of NO2 and airway responsiveness to inform a decision on
standard level, the Administrator notes the following:
NO2-induced increases in airway responsiveness,
as reported in controlled human exposure studies, are logically linked
to the adverse respiratory effects that have been reported in
NO2 epidemiologic studies.
The meta-analysis of controlled human exposure data in the
ISA reported increased airway responsiveness in a large percentage of
asthmatics at rest following exposures at and above 100 ppb
NO2, the lowest NO2 concentration for which
airway responsiveness data are available in humans.
This meta-analysis does not provide any evidence of a
threshold below which effects do not occur. The studies included in the
meta-analysis evaluated primarily mild asthmatics while more severely
affected individuals could respond to lower concentrations. Therefore,
it is possible that exposure to NO2 concentrations below 100
ppb could increase airway responsiveness in some asthmatics.
In considering the evidence, the Administrator recognizes that the
NO2-induced increases in airway responsiveness reported for
exposures to NO2 concentrations at or above 100 ppb could be
adverse for some asthmatics. However, she also notes that important
uncertainties exist with regard to the extent to which NO2-
induced increases in airway responsiveness are adverse. Specifically,
she notes the following with regard to these uncertainties:
The magnitude of the NO2-induced increase in
airway responsiveness, and the extent to which it is adverse, cannot be
quantified from the ISA meta-analysis (REA, section 10.3.2.1).
The NO2-induced increase in airway
responsiveness in resting asthmatics was typically not accompanied by
increased respiratory symptoms, even following exposures to
NO2 concentrations well above 100 ppb (ISA, section
3.1.3.3).
The increase in airway responsiveness that was reported
for resting asthmatics was not present in exercising asthmatics (ISA,
Table 3.1-3).
Taking into consideration all of the above, the Administrator
concludes that existing evidence supports the conclusion that the
NO2-induced increase in airway responsiveness at or above
100 ppb presents a risk of adverse
[[Page 6501]]
effects for some asthmatics, especially those with more serious (i.e.,
more than mild) asthma. The Administrator notes that the risks
associated with increased airway responsiveness cannot be fully
characterized by these studies, and thus she is not able to determine
whether the increased airway responsiveness experienced by asthmatics
in these studies is an adverse health effect. However, based on these
studies the Administrator concludes that asthmatics, particularly those
suffering from more severe asthma, warrant protection from the risk of
adverse effects associated with the NO2-induced increase in
airway responsiveness. Therefore, the Administrator concludes that the
controlled human exposure evidence supports setting a standard level no
higher than 100 ppb to reflect a cautious approach to the uncertainty
regarding the adversity of the effect. However, those uncertainties
lead her to also conclude that this evidence does not support setting a
standard level lower than 100 ppb.
In considering the more serious health effects reported in
NO2 epidemiologic studies, as they relate to the level of a
standard that reflects the maximum allowable NO2
concentration anywhere in an area, the Administrator notes the
following:
A cluster of 5 key U.S. epidemiologic studies (Ito et al.,
2007; Jaffe et al., 2003; Peel et al., 2005; Tolbert et al., 2007; and
a study by the New York State Department of Health, 2006) provide
evidence for associations between NO2 and respiratory-
related emergency department visits and hospital admissions in
locations where 98th percentile 1-hour daily maximum NO2
concentrations measured at area-wide monitors ranged from 85 to 94 ppb.
The Administrator judges it appropriate to place substantial weight on
this cluster of key U.S. epidemiologic studies in selecting a standard
level, as they are a group of studies that reported positive, and often
statistically significant, associations between NO2 and
respiratory morbidity in multiple cities across the United States.\20\
---------------------------------------------------------------------------
\20\ Some of these studies also included susceptible and
vulnerable populations (e.g., children in Peel et al. (2005); poor
and minority populations in Ito et al., 2007).
---------------------------------------------------------------------------
A single study (Delfino et al., 2002) provides mixed
evidence for NO2 effects (i.e., respiratory symptoms) in a
location with a 98th percentile 1-hour daily maximum NO2
concentration, as measured by an area-wide monitor, of 50 ppb. In that
study, most of the reported NO2 effect estimates were
positive, but not statistically significant. Given the variability in
the NO2 effect estimates in this study, as well as the lack
of studies in other locations with similarly low NO2
concentrations, the Administrator judges it appropriate to place
limited weight on this study, compared to the cluster of 5 studies as
noted above.
Given these considerations, the Administrator concludes that the
epidemiologic evidence provides strong support for setting a standard
that limits the 98th percentile of the distribution of 1-hour daily
maximum area-wide NO2 concentrations to below 85 ppb. This
judgment takes into account the determinations in the ISA, based on a
much broader body of evidence, that there is a likely causal
association between exposure to NO2 and the types of
respiratory morbidity effects reported in these studies. Given the
considerations discussed above, the Administrator judges that it is not
necessary, based on existing evidence, to set a standard that maintains
peak area-wide NO2 concentrations to below 50 ppb.
In considering specific standard levels supported by the
epidemiologic evidence, the Administrator notes that a level of 100
ppb, for a standard reflecting the maximum allowable NO2
concentration anywhere in the area, would be expected to maintain area-
wide NO2 concentrations well below 85 ppb, which is the
lowest 98th percentile concentration in the cluster of 5 studies. With
regard to this, she specifically notes the following:
If NO2 concentrations near roads are 100%
higher than concentrations away from roads, a standard level of 100 ppb
would limit area-wide concentrations to approximately 50 ppb.
If NO2 concentrations near roads are 30% higher
than concentrations away from roads, a standard level of 100 ppb would
limit area-wide concentrations to approximately 75 ppb.
The Administrator has also considered the NO2 exposure
and risk information within the context of the above conclusions on
standard level. Specifically, she notes that the results of exposure
and risk analyses were interpreted as providing support for limiting
area-wide NO2 concentrations to no higher than 100 ppb.
Specifically, these analyses estimated that a standard that limits
area-wide NO2 concentrations to approximately 100 ppb or
below would be expected to result in important reductions in
respiratory risks, relative to the level of risk permitted by the
current annual standard alone. As discussed above, a standard
reflecting the maximum allowable NO2 concentration with a
level of 100 ppb would be expected to maintain area-wide NO2
concentrations to within a range of approximately 50 to 75 ppb. Given
this, the Administrator concludes that a standard level of 100 ppb is
consistent with conclusions based on the NO2 exposure and
risk information.
Finally, the Administrator notes that a standard level of 100 ppb
is consistent with the consensus recommendation of CASAC.
Given the above considerations and the comments received on the
proposal, the Administrator determines that the appropriate judgment,
based on the entire body of evidence and information available in this
review, and the related uncertainties, is a standard level of 100 ppb
(for a standard that reflects the maximum allowable NO2
concentration anywhere in an area). She concludes that such a standard,
with the averaging time and form discussed above, will provide a
significant increase in public health protection compared to that
provided by the current annual standard alone and would be expected to
protect against the respiratory effects that have been linked with
NO2 exposures in both controlled human exposure and
epidemiologic studies. Specifically, she concludes that such a standard
will limit exposures at and above 100 ppb for the vast majority of
people, including those in at-risk groups, and will maintain maximum
area-wide NO2 concentrations well below those in locations
where key U.S. epidemiologic studies have reported that ambient
NO2 is associated with clearly adverse respiratory health
effects, as indicated by increased hospital admissions and emergency
department visits.
In setting the standard level at 100 ppb rather than a lower level,
the Administrator notes that a 1-hour standard with a level lower than
100 ppb would only result in significant further public health
protection if, in fact, there is a continuum of serious, adverse health
risks caused by exposure to NO2 concentrations below 100 ppb
and/or associated with area-wide NO2 concentrations well-
below those in locations where key U.S. epidemiologic studies have
reported associations with respiratory-related emergency department
visits and hospital admissions. Based on the available evidence, the
Administrator does not believe that such assumptions are warranted.
Taking into account the uncertainties that remain in interpreting the
evidence from available controlled human exposure and epidemiologic
studies, the Administrator notes that the likelihood of obtaining
benefits to public health with a standard set below
[[Page 6502]]
100 ppb decreases, while the likelihood of requiring reductions in
ambient concentrations that go beyond those that are needed to protect
public health increases.
Therefore, the Administrator judges that a standard reflecting the
maximum allowable NO2 concentration anywhere in an area set
at 100 ppb is sufficient to protect public health with an adequate
margin of safety, including the health of at-risk populations, from
adverse respiratory effects that have been linked to short-term
exposures to NO2 and for which the evidence supports a
likely causal relationship with NO2 exposures. The
Administrator does not believe that a lower standard level is needed to
provide this degree of protection. These conclusions by the
Administrator appropriately consider the requirement for a standard
that is neither more nor less stringent than necessary for this purpose
and recognizes that the CAA does not require that primary standards be
set at a zero-risk level or to protect the most sensitive individual,
but rather at a level that reduces risk sufficiently so as to protect
the public health with an adequate margin of safety.
G. Annual Standard
In the proposal, the Administrator noted that some evidence
supports a link between long-term exposures to NO2 and
adverse respiratory effects and that CASAC recommended in their
comments prior to the proposal that, in addition to setting a new 1-
hour standard to increase public health protection, the current annual
standard be retained. CASAC's recommendation was based on the
scientific evidence and on their conclusion that a 1-hour standard
might not provide adequate protection against exposure to long-term
NO2 concentrations (Samet, 2008b).
With regard to an annual standard, CASAC and a large number of
public commenters (e.g., NACAA, NESCAUM; agencies from States including
CA, IN, MO, NC, NY, SC, TX, VA; Tribal organizations including Fon du
Lac and the National Tribal Air Organization; environmental/medical/
public health groups including ACCP, ALA, AMA, ATS, CAC, EDF, EJ, GASP,
NACPR, NAMDRC, NRDC) agreed with the proposed decision to maintain an
annual standard, though their recommendations with regard to the level
of that annual standard differed (see below).
As noted above, CASAC recommended ``retaining the current standard
based on the annual average'' based on the ``limited evidence related
to potential long-term effects of NO2 exposure and the lack
of strong evidence of no effect'' and that ``the findings of the REA do
not provide assurance that a short-term standard based on the one-hour
maximum will necessarily protect the population from long-term
exposures at levels potentially leading to adverse health effects''
(Samet, 2008b). A number of State agencies and organizations also
recommended maintaining the current level of the annual standard (i.e.,
53 ppb). This recommendation was based on the conclusion that, while
some evidence supports a link between long-term NO2
exposures and adverse respiratory effects, that evidence is not
sufficient to support a standard level either higher or lower than the
current level. In addition, a number of industry groups (e.g., AAM,
API, Dow, INGAA, UARG) recommended retaining the level of the current
annual standard but, as described above, did so within the context of a
recommendation that EPA should not set a new 1-hour standard.
In contrast, some environmental organizations and medical/public
health organizations as well as a small number of States (e.g., ALA,
EDF, EJ, NRDC, and organizations in CA) recommended setting a lower
level for the annual standard. These commenters generally supported
their recommendation by pointing to the State of California's annual
standard of 30 ppb and to studies where long-term ambient
NO2 concentrations have been associated with adverse
respiratory effects such as impairments in lung function growth.
As discussed above (II.B.3), the evidence relating long-term
NO2 exposures to adverse health effects was judged in the
ISA to be either ``suggestive but not sufficient to infer a causal
relationship'' (respiratory morbidity) or ``inadequate to infer the
presence or absence of a causal relationship'' (mortality, cancer,
cardiovascular effects, reproductive/developmental effects) (ISA,
sections 5.3.2.4-5.3.2.6). In the case of respiratory morbidity, the
ISA (section 5.3.2.4) concluded that ``The high correlation among
traffic-related pollutants made it difficult to accurately estimate the
independent effects in these long-term exposure studies.'' Given these
uncertainties associated with the role of long-term NO2
exposures in causing the reported effects, the Administrator concluded
in the proposal that, consistent with the CASAC recommendation,
existing evidence is not sufficient to justify setting an annual
standard with either a higher or lower level than the current standard.
Commenters have not submitted any new analyses or information that
would change this conclusion. Therefore, the Administrator does not
agree with the commenters who recommended a lower level for the annual
standard.
The Administrator judges that her conclusions in the proposal
regarding the annual standard remain appropriate. Specifically, she
continues to agree with the conclusion that, though some evidence does
support the need to limit long-term exposures to NO2, the
existing evidence for adverse health effects following long-term
NO2 exposures does not support either increasing or
decreasing the level of the annual standard. In light of this and
considering the recommendation from CASAC to retain the current level
of the annual standard, the Administrator judges it appropriate to
maintain the level of the annual standard at 53 ppb.
H. Summary of Final Decisions on the Primary NO2 Standard
For the reasons discussed above, and taking into account
information and assessments presented in the ISA and REA, the advice
and recommendations of the CASAC, and public comments, the
Administrator has decided to revise the existing primary NO2
standard. Specifically, the Administrator has determined that the
current annual standard by itself is not requisite to protect public
health with an adequate margin of safety. In order to provide
protection for asthmatics and other at-risk populations against an
array of adverse respiratory health effects related to short-term
NO2 exposure, the Administrator is establishing a short-term
NO2 standard defined by the 3-year average of the 98th
percentile of the yearly distribution of 1-hour daily maximum
NO2 concentrations. She is setting the level of this
standard at 100 ppb, which is to reflect the maximum allowable
NO2 concentration anywhere in an area. In addition to
setting a new 1-hour standard, the Administrator retains the current
annual standard with a level of 53 ppb. The new 1-hour standard, in
combination with the annual standard, will provide protection for
susceptible groups against adverse respiratory health effects
associated with short-term exposures to NO2 and effects
potentially associated with long-term exposures to NO2.
III. Amendments to Ambient Monitoring and Reporting Requirements
The EPA is finalizing several changes to the ambient air
monitoring, reporting, and network design requirements for the
NO2 NAAQS. This section discusses the changes we are
finalizing which are intended to support the proposed 1-
[[Page 6503]]
hour NAAQS and retention of the current annual NAAQS as discussed in
Section II. Ambient NO2 monitoring data are used to
determine whether an area is in violation of the NO2 NAAQS.
Ambient NO2 monitoring data are collected by State, local,
and Tribal monitoring agencies (``monitoring agencies'') in accordance
with the monitoring requirements contained in 40 CFR parts 50, 53, and
58.
A. Monitoring Methods
We are finalizing the proposed changes regarding the NO2
Federal Reference Method (FRM) or Federal Equivalent Method (FEM)
analyzers. Specifically, we are continuing to use the NO2
chemiluminescence FRM and are finalizing the requirement that any
NO2 FRM or FEM used for making primary NAAQS decisions must
be capable of providing hourly averaged concentration data. The
following paragraphs provide background and rationale for the continued
use of the chemiluminescence FRM and the decision to finalize the
proposed changes.
1. Chemiluminescence FRM and Alternative Methods
The current monitoring method in use by most State and local
monitoring agencies is the gas-phase chemiluminescence FRM (40 CFR Part
50, Appendix F), which was implemented into the NO2
monitoring network in the early 1980s. EPA did not propose to
discontinue using the chemiluminescence FRM, although we received some
comments from industry (Alliance of Automobile Manufacturers, Edison
Electric, and the National Petrochemical and Refiners Association)
raising concerns about using a method that is subject to known
interferences from certain species of oxides of nitrogen known as
NOZ. Important components of ambient NOZ include
nitrous acid (HNO2), nitric acid (HNO3), and the
peroxyacetyl nitrates (PANs).
The issue of concern in public comments is that the reduction of
NO2 to NO on the MoOX converter substrate used in
chemiluminescence FRMs is not specific to NO2; hence,
chemiluminescence method analyzers are subject to varying interferences
produced by the presence in the air sample of the NOZ
species listed above and others occurring in trace amounts in ambient
air. This interference is often termed a ``positive artifact'' in the
reported NO2 concentration since the presence of
NOZ results in an over-estimate in the reported measurement
of the actual ambient NO2 concentration. This interference
by NOZ compounds has long been known and evaluated
(Fehsenfeld et al., 1987; Nunnermacker et al., 1998; Parrish and
Fehsenfeld, 2000; McClenny et al., 2002; U.S. Environmental Protection
Agency, 1993, 2006a). Further, as noted in the ISA (ISA Section 2.3),
it appears that interference by NOZ on chemiluminescence
FRMs is not more than 10 percent of the reported NO2
concentration during most or all of the day during winter (cold
temperatures), but larger interference ranging up to 70 percent can be
found during summer (warm temperatures) in the afternoon at sites away
and downwind from strong emission sources.
The EPA acknowledges that the NOZ interference in the
reported NO2 concentrations collected well downwind of
NOX source areas and in relatively remote areas away from
concentrated point, area, or mobile sources is significantly larger
than the NOZ interference in NO2 measurements
taken in urban cores or other areas with fresh NOX
emissions. To meet the primary objective of monitoring maximum
NO2 concentrations in an area, the EPA is requiring
NO2 monitors to be placed in locations of the expected
highest concentrations, not in relatively remote areas away from
NOX sources. The required monitors resulting from the
network design discussed below in Section III.B will require monitors
to be placed near fresh NOX sources or in areas of dense
NOX emissions, where NO2 concentrations are
expected to be at a maximum, and interference from NOZ
species is at a minimum. Therefore, EPA believes that the positive
artifact issue, although present, is small, relative to the actual
NO2 being measured. As a result EPA believes the
chemiluminescence FRM is suitable for continued use in the ambient
NO2 monitoring network, as the potential positive bias from
NOZ species is not significant enough to discontinue using
the chemiluminescence FRM.
EPA also received support from some industry groups (e.g. Savannah
River Nuclear Solutions, Teledyne API, and the Utility Air Regulatory
Groups) and States (e.g., MODEQ and NCDENR) to further the development
of alternative methods in determining NO2 concentrations.
Such alternative methods include the photolytic- chemiluminescence
method and cavity ring-down spectroscopy. As a result, EPA will
continue working with commercial and industrial vendors, to identify
and evaluate such new technologies. These efforts may include field
testing instruments and further characterizing methods in a laboratory
setting to assess their potential as future reference or equivalent
methods, and their role in more directly measuring NO2.
2. Allowable FRM and FEMs for Comparison to the NAAQS
The current CFR language does not prohibit the use of any
particular NO2 FRM or FEM to be used in comparison to the
standard.\21\ There are designated wet chemical methods that are only
able to report ambient concentration values averaged across multiple
hours. With the establishment of a 1-hour NAAQS, any FRM or FEM which
is a wet chemical based method would not be appropriate for use in
determining compliance of the 1-hour NAAQS because they are unable to
report hourly data. EPA addressed this issue by proposing and
finalizing that only those methods capable of providing 1-hour
measurements will be comparable to the NAAQS.
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\21\ A list of approved FRM and FEMs is maintained by EPA's
Office of Research and Development, and can be found at: http://www.epa.gov/ttn/amtic/files/ambient/criteria/reference-equivalent-methods-list.pdf.
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a. Proposed Changes to FRM and FEMs That May Be Compared to the NAAQS
EPA proposed that only those FRMs or FEMs that are capable of
providing hourly averaged concentration data may be used for comparison
to the NAAQS.
b. Comments
EPA received comments from some State and industry groups (e.g.
Missouri, North Carolina, and Air Quality Research and Logistics)
supporting the proposed approach to only allowing those FRMs or FEMs
that are capable of providing hourly averaged concentration data may be
used for comparison to both the annual and 1-hour NAAQS, and did not
receive any public comments that objected to the proposed approach.
c. Decisions on Allowable FRM and FEMs for Comparison to the NAAQS
Accordingly, EPA is finalizing the proposed changes to 40 CFR Part
58 Appendix C to allow only data from FRM or FEMs that are capable of
providing hourly data to be used for comparison to both the annual and
1-hour NAAQS.
B. Network Design
With the establishment of a 1-hour NO2 NAAQS intended to
limit exposure to maximum concentrations that may occur anywhere in an
area, EPA recognizes that the data from the current NO2
network is inadequate to fully assess compliance with the revised
[[Page 6504]]
NAAQS. As a result, EPA is promulgating new NO2 network
design requirements. The following sections provide background,
rationale, and details for the final changes to the NO2
network design requirements.
1. Two-Tiered Network Design
A two-tiered monitoring network is appropriate for the
NO2 NAAQS because one tier (the near-road network) reflects
the much higher NO2 concentrations that occur near-road and
the second-tier (area-wide) characterizes the NO2
concentrations that occur in a larger area such as neighborhood or
urban areas. The ISA (Section 2.5.4 and 4.3.6) stated that
NO2 concentrations in heavy traffic or on freeways ``can be
twice the residential outdoor or residential/arterial road level,''
that ``exposure in traffic can dominate personal exposure to
NO2,'' and that ``NO2 levels are strongly
associated with distance from major roads (i.e., the closer to a major
road, the higher the NO2 concentration).'' The exposure
assessment presented in the REA estimated that roadway-associated
exposures account for the majority of exposures to peak NO2
concentrations (REA, Figures 8-17, 8-18). Monitoring studies suggest
that NO2 concentrations near roads can be considerably
higher than those in the same area but away from the road (e.g., by 30-
100%, see section II.A.2), where pollutants typically display peak
concentrations on or immediately adjacent to roads, producing a
gradient in pollutant concentrations where concentrations decrease with
increasing distance from roads. Since the intent of the revised NAAQS
is to limit exposure to peak NO2 concentrations that occur
anywhere in an area, monitors intended to measure the maximum allowable
NO2 concentration in an area should include measurements of
the peak concentrations that occur on and near roads due to on-road
mobile sources. The first tier of the network design, which focuses
monitoring near highly trafficked roads in urban areas where peak
NO2 concentrations are likely to occur, is intended to
measure maximum concentrations anywhere in an area, particularly those
due to on-road mobile sources since roadway-associated exposures
account for the majority of exposures to peak NO2
concentrations. The basis for the second tier of the network design is
to measure the highest area-wide concentrations to characterize the
wider area impact of a variety of NO2 sources on urban
populations. Area-wide monitoring of NO2 also serves to
maintain continuity in collecting data to inform long-term pollutant
concentration trends analysis and support ongoing health and scientific
research.
This section discusses the two-tier network design approach
compared to the alternative network design which was also presented for
comment in conjunction with a solicitation for comment on an
alternative NAAQS. The alternative network design concept was based
entirely on requiring only monitors that would be considered area-wide,
while not requiring any near-road monitoring sites. The details of the
two-tier network design, including how many monitors are required,
where they are to be located, and the related siting criteria are
discussed in subsequent sections.
a. Proposed Two-Tier Network Design
EPA proposed a two-tier network design composed of (1) near-road
monitors which would be placed in locations of expected maximum 1-hour
NO2 concentrations near heavily trafficked roads in urban
areas and (2) monitors located to characterize areas with the highest
expected NO2 concentrations at the neighborhood and larger
spatial scales (also referred to as ``area-wide'' monitors). As an
alternative, and in conjunction with a solicitation for comment on an
alternative NAAQS, EPA solicited comment on a network comprised of only
area-wide monitors.
b. Comments
EPA received many comments on the overall two-tier network design,
with those who made statements with a relatively clear position on the
issue generally falling into four categories: (1) Those who support the
adoption of the proposed two-tier design approach, (2) those who
support the adoption of the two-tier concept, but with modifications,
(3) those who only supported the adoption of the alternative network
design, and (4) those who encourage EPA to commit to further research
of the near-road environment by monitoring near-roads, but not to use
near-road data for regulatory purposes, and therefore support the
alternative network design in which EPA solicited comment on a network
design composed only of area-wide monitors.
Those commenters who generally supported the proposed two-tier
network, included CASAC (while there was not a consensus, a majority
were in support of the proposed network design), public health
organizations (e.g., AACPR, ACCP, AMA, ATA, and NAMDRC), several State
groups (e.g., the New York City Law Department and the Metropolitan
Washington Air Quality Committee), and some industry commenters (e.g.,
American Chemistry Council, The Clean Energy Group, and Dow Chemical).
Those commenters who supported the adoption of the two-tier network
design concept, but suggested modifications to the actual design
included some health and environmental organizations (e.g., ALA, EDF,
EJ, and the NRDC), some States (e.g., California, the Central
Pennsylvania Clean Air Board, Harris County (Texas), Iowa, New York,
San Joaquin Air Pollution Control District, Spokane Regional Clean Air
Agency (SRCAA), the Texas Commission on Environmental Quality, and
Wisconsin), and some industry commenters, including the American
Petroleum Institute and the Utility Air Regulatory Group, who are cited
by other industry commenters. We believe that although these commenters
made suggestions to modify the proposed two-tier network design, they
are indicating that it is an acceptable approach. Their comments and
suggestions are discussed in greater detail in the following sections.
Those commenters who only supported the adoption of the alternative
network design included State and industry groups (e.g., Indiana
Department of Environmental Management, the New York Department of
Transportation (NYSDOT), Alliance of Automobile Manufacturers, and the
Engine Manufacturers Association). These commenters typically made
comments on the two-tier network design, but did not do so in a way
that clearly supported near-road research.
EPA received comments from some States or State organizations
(e.g., National Association of Clean Air Agencies (NACAA), the
Northeast States for Coordinated Air Use Management (NESCAUM), and 10
other individual States or State groups) and industry commenters (e.g.,
Consumers Energy, Edison Electric, and the National Association of
Manufacturers) that encouraged EPA to further research the near-road
environment, opposing use of near-road monitoring data for regulatory
purposes, and supported the adoption of the alternative network design
for regulatory purposes. For example, with regard to implementing the
two-tier network design that includes near-road regulatory monitoring,
NACAA stated that ``* * *a major new network--particularly one that is
inherently complicated and untried--should not be rolled out without
the benefit of an effective near-road monitoring research program that
can address many of the relevant data questions, and inform the
specific siting requirements of the rule.'' The NAM stated that
``conducting such
[[Page 6505]]
a near road [research] monitoring program would allow EPA to collect
necessary data that can be used to better understand the health impacts
associated with short term NO2 exposures.''
The EPA notes that the existing scientific research referenced in
the proposal and throughout this final rule show that there are on- and
near-road peaks of NO2 concentrations, relative to upwind or
background levels, which exist due to on-road mobile source emissions.
This research, as a body of evidence, also identifies the multiple
local factors that affect how, where, and when peak NO2
concentrations occur on or near a particular road segment. These
factors include traffic volume, fleet mix, roadway design, congestion
patterns, terrain, and meteorology. The EPA and States have access to
such data typically through Federal, State, and/or local departments of
transportation or other government organizations, and, as a result, are
in a position to implement a near-roar monitoring network that is
intended to measure maximum expected NO2 concentrations
resulting from on-road mobile source emissions. Further, EPA notes that
near-road monitoring is not a new objective for the ambient air
monitoring community as near-road carbon monoxide monitoring has been a
part of ongoing, long-term, routine networks for nearly three decades.
As a result, there is experience within EPA (both OAR and ORD) and
State and local agencies on conducting ambient monitoring near-roads.
In addition, EPA intends to develop guidance with input from all
stakeholders to assist with implementation of the monitoring
requirements, which is discussed in section III.B.5. EPA believes that
the existing science and research provide a sufficient base of
information to require a near-road monitoring network and that the
collective experience that exists in the ambient monitoring community
will allow for successful implementation of that network. EPA also
believes that through adherence of requirements for near-road site
selection and siting criteria discussed in sections III.B.6 and
III.B.7, respectively, that the two-tier network design will provide a
network that has a reasonable degree of similarity across the country
where the required near-road monitors are targeting the maximum
NO2 concentrations in an area attributable to on-road mobile
sources.
Some industry commenters (e.g., Engine Manufacturers Association,
the South Carolina Chamber of Commerce, and the South Carolina
Manufacturers Alliance) who supported the adoption of the alternative
network design suggested that monitoring in the near-road environment
would not be indicative of exposure for general populations, and that
EPA should not focus on the near-road environment when requiring
monitoring. For example, the South Carolina Chamber of Commerce and the
South Carolina Manufacturers Alliance both state that ``it appears the
proposed monitoring network will result in a collection of microscale
data, which is not at all representative of air quality relevant to
population exposure.''
The EPA notes that the intent of a near-road monitoring is to
support the revised NAAQS by assessing peak NO2
concentrations that may occur anywhere in an area. EPA recognizes that
there is variability in the properties (such as traffic counts, fleet
mix, and localized features) among the road segments that may exist in
an area, but on the whole, roads are ubiquitous, particularly in urban
environments. Consequently, a substantial fraction of the population is
potentially exposed to relatively higher concentrations of
NO2 that can occur in the near-road environment. The 2007
American Housing Survey (http://www.census.gov/hhes/www/housing/ahs/ahs07/ahs07.html) estimates that over 20 million housing units are
within 300 feet (91 meters) of a 4-lane highway, airport, or railroad.
Using the same survey, and considering that the average number of
residential occupants in a housing unit is approximately 2.25, it is
estimated that at least 45 million American citizens live near 4-lane
highways, airports, or railroads. Although that survey includes
airports and railroads, roads are the most pervasive of the three,
indicating that a significant amount of the general population live
near roads. Furthermore, the 2008 American Time Use Survey (http://www.bls.gov/tus/) reported that the average U.S. civilian spent over 70
minutes traveling per day. Accordingly, EPA concludes that monitors
near major roads will address a component of exposure for a significant
portion of the general population that would otherwise not be
addressed.
The majority of State commenters, regardless of their position on
the proposed network design, along with some industry commenters,
observed that there was a need for funding the monitoring network.
These comments urged EPA to provide the resources needed to implement
and operate the required monitoring network. EPA notes that it has
historically funded part of the cost of the installation and operation
of monitors used to satisfy Federal monitoring requirements. EPA
understands these concerns, although the CAA requirements from which
this final rule derives (CAA sections 110, 310(a) and 319) are not
contingent on EPA providing funding to States to assist in meeting
monitoring requirements. However, EPA intends to work with NACAA and
the State and local air agencies in identifying available State and
Tribal Air Grant (STAG) funds and consider the increased resource needs
that may be needed to plan, implement, and operate this revised set of
minimum requirements.
c. Conclusions Regarding the Two-Tier Network Design
The EPA believes that requiring near-road monitors in urban areas
as part of the network design are necessary to protect against risks
associated with exposures to peak concentrations of NO2
anywhere in an area. The combination of increased mobile source
emissions and increased urban population densities can lead to
increased exposures and associated risks, therefore urban areas are the
appropriate areas to concentrate required near-road monitoring efforts.
The EPA also recognizes the need to have monitors in neighborhood and
larger spatial scale locations away from roads that represent area-wide
concentrations. These types of monitors serve multiple important
monitoring objectives including comparison to the NAAQS, photochemical
pollutant assessment, ozone forecasting, characterization of point and
area source impacts, and by providing historical trends data for
current and future epidemiological health research. In some situations,
when coupled with data from near-road monitors, area-wide monitors may
also assist in the determination of spatial variation of NO2
concentrations across a given area and provide insight to the gradients
that exist between near-road or stationary source oriented
concentrations and area-wide concentration levels.
After considering the scientific data and the public comments
regarding the proposed network design, the Administrator concludes that
a two-tier network design composed of (1) near-road monitors which
would be placed in locations of expected maximum 1-hour NO2
concentrations near heavily trafficked roads in urban areas and (2)
monitors located to characterize areas with the maximum expected
NO2 concentrations at the neighborhood and larger spatial
scales (also referred to as ``area-wide'' monitors) are needed to
implement the 1-hour NO2 NAAQS and
[[Page 6506]]
support the annual NAAQS. The details of this two-tier network design
are discussed in the following eight sections.
2. First Tier (Near-Road Monitoring Component) of the NO2
Network Design
This section provides background, rationale, and details for the
final changes to the first tier of the two-tier NO2 network
design. In particular, this section will focus on the thresholds that
trigger monitoring requirements. Near-road site selection and siting
criteria details will be discussed in subsequent sections.
a. Proposed First Tier (Near-Road Monitoring Component) of the Network
Design
EPA proposed that the first tier of the two-tier NO2
monitoring network design focus monitors in locations of expected
maximum 1-hour concentrations near major roads in urban areas. As noted
in the previous section, the exposure assessment presented in the REA
estimated that roadway-associated exposures account for the majority of
exposures to peak NO2 concentrations (REA, Figures 8-17, 8-
18). Since the combination of increased mobile source emissions and
increased urban population densities leads to increased exposures and
associated risks, the Administrator judges that urban areas are the
appropriate areas in which to concentrate required near-road monitoring
efforts. Therefore, we proposed that a minimum of one near-road
NO2 monitor be required in Core Based Statistical Areas
(CBSAs) with a population greater than or equal to 350,000 persons.
Based on 2008 Census Bureau statistics, EPA estimated this would result
in approximately 143 monitoring sites in as many CBSAs.
We also proposed that a second near-road monitor be required in
CBSAs with a population greater than or equal to 2,500,000 persons, or
in any CBSAs with one or more road segments with an Annual Average
Daily Traffic (AADT) count greater than or equal to 250,000. Based on
2008 Census Bureau statistics and data from the 2007 Highway
Performance Monitoring System (HPMS) maintained by the U.S. Department
of Transportation (DOT) Federal Highway Administration (FHWA), this
particular element of the minimum monitoring requirements would have
added approximately 24 \22\ sites to the approximate 143 near-road
sites in CBSAs that already would have had one near-road monitor
required due to the 350,000 population threshold. Overall, the first
tier of the proposed network design was estimated to require 167 near-
road sites in 143 CBSAs.
---------------------------------------------------------------------------
\22\ Of the 24 additional sites, 22 are estimated to be
triggered due to a population of 2,500,000 while 2 (Las Vegas, NV
and Sacramento, CA) are estimated to be triggered by the presence of
one or more road segments with 250,000 AADT since they do not have a
population of 2,500,000 people.
---------------------------------------------------------------------------
b. Comments
The EPA received comments from some industry and public health
organizations (e.g. Dow Chemical, ATS, and the AMA) supporting the
proposed approach to use population thresholds for triggering minimum
near-road monitoring requirements. For example, Dow Chemical Company
stated that ``Dow comments that the proposed population thresholds are
reasonable for implementation of the new network design and that we
don't see a need to establish a threshold lower than 350,000 people for
the lower bound.''
The EPA received comments from some States and State groups
suggesting that a combination of population and AADT counts or just
AADT counts should be used to trigger minimum near-road monitoring
requirements. For example, the San Joaquin Air Pollution Control
District in California suggested that we modify minimum monitoring
requirements so that one near-road NO2 monitor is required
for any CBSA with a population of 350,000 people which also had one or
more road segments with AADT counts of 125,000 or more. In another
example, Harris County Public Health and Environmental Services
(HCPHES) suggested that ``* * * rather than specifying population
limits for the monitoring, HCPHES supports a metric like the Annual
Average Daily Traffic (AADT) as a threshold for requiring a near-road
monitor. An initial focus on an AADT in excess of 250,000 is acceptable
as a starting point but EPA should revisit that level and consider
lowering it to 100,000 in five years.'' AASHTO \23\ and NYDOT \23\
suggested that EPA could set a threshold at 140,000 AADT for requiring
near-road monitors rather than using population thresholds.
---------------------------------------------------------------------------
\23\ AASHTO, NESCAUM, and NYDOT did not support the two-tier
network design; however they provided suggestions on how the network
design might be modified if the EPA were to finalize requirements
for near-road monitors. In the case of AASHTO and NYDOT, their
suggestions were made with the suggestion that EPA use a separate
rulemaking process to require monitors.
---------------------------------------------------------------------------
EPA is finalizing the population-only threshold approach to trigger
near-road monitoring, as the first step in the process of establishing
the first-tier of near-road monitors, and for identifying the
appropriate number and locations for siting these monitors. EPA
believes that the uncertainty in defining specific national AADT counts
is too great to support use in this first step of the alternative
approaches suggested by the commenters. EPA notes that, in general,
roads with higher AADT counts have relatively higher amounts of mobile
source emissions, leading to an increased potential for relatively
higher on-road and roadside NO2 concentrations. This concept
is supported, for example, by Gilbert et al., 2007, who state that the
NO2 concentrations analyzed in their study are significantly
associated with traffic counts. In part, these suggestions by
commenters to include AADT counts as part of, or independently as, a
threshold for requiring monitors appears to be aimed at increasing the
focus of the near-road network to locations where NO2
concentrations are expected to be highest. However these suggestions
would also, in effect, reduce the size of the required network compared
to the network that EPA had proposed. The differences in fleet mix,
roadway design, congestion patterns, terrain, and local meteorology
amongst road segments that may have identical AADTs are quite variable
and affect the NO2 concentrations on and near those
segments. The available data and related technical and scientific
quantification of what particular AADT count might be expected to
contribute to some specific NO2 concentration is
insufficient to establish a specific, nationally applicable AADT count
threshold that could be used as part of a population-AADT combination,
or a distinct AADT count, to require all near-road monitors. Therefore,
EPA chose not to utilize a population-AADT or an AADT-only threshold to
trigger all minimally required near-road monitoring because of the lack
of a quantitative, nationally applicable relationship between a certain
AADT threshold and an expected NO2 concentration. Instead,
EPA is finalizing the proposed population-only threshold approach to
trigger a minimum of one monitor in a CBSA. In larger CBSAs, EPA does
require, at a minimum, a second monitor based on either an AADT count
of 250,000 or a population threshold of 2,500,00 or more persons in a
CBSA as described more fully below. EPA believes this approach for
siting near-road monitoring provides a greater degree of certainty in
covering a large segment of the total population (66%, which is
explained below) and will provide data on exposure from geographically
and spatially diverse areas where a larger number of people
[[Page 6507]]
are likely to be exposed to peak NO2 concentrations.
Some commenters (e.g., AASHTO,\23\ NESCAUM,\23\ NYDEC, NYDOT \23\)
suggested focusing multiple near-road monitors only in relatively
larger CBSAs than those which were proposed. For example, NYDEC
suggested that EPA require, at minimum, two near-road monitors in any
CBSA of 2,500,000 people or more, but not in CBSAs below that
population threshold. In their comments, they point out the variety of
near-road environments that exist in the larger CBSAs such as New York
City.
EPA notes that the larger CBSAs, such as those with a population of
2,500,000 or more persons, are more likely to have a greater number of
major roads across a potentially larger geographic area, and a
corresponding increase in potential for exposure in different settings
(evidenced in the U.S. Department of Transportation (U.S. DOT) Federal
Highway Administration (FHWA) ``Status of the Nation's Highways,
Bridges, and Transit: 2006 Conditions and Performance'' document which
is discussed below). This is the primary reasoning behind the
requirement for two monitors in CBSAs with more than 2,500,000 people.
EPA also believes that having multiple monitors in the largest CBSAs
will allow better understanding of the differences that may exist
between roads in the same CBSA due to fleet mix, congestion patterns,
terrain, or geographic locations. However, EPA believes that a network
with substantially fewer monitors in correspondingly fewer CBSAs, as
the commenters suggested, would lead to an insufficient monitoring
network lacking a balanced approach needed for a regulatory network
intended to support the revised NAAQS on a national basis.
On a related note to those comments that suggested focusing more
near-road monitors only in the larger CBSAs, EPA proposed that any
CBSAs with one or more road segments with an Annual Average Daily
Traffic (AADT) count greater than or equal to 250,000 must have a
second monitor if they do not already have two near-road monitors
because of the population threshold. Such an AADT-triggered monitor
would account for situations where a relatively less populated area has
a very highly trafficked road. In this case, EPA notes that because
those road segments with 250,000 AADT have been identified by U.S. DOT
FHWA (http://www.fhwa.dot.gov/policyinformation/tables/02.cfm) as being
the top 0.03 percent of the most traveled public road segments, that
they are the most heavily trafficked roads in the country. Again noting
that NO2 concentrations are significantly associated with
traffic counts (Gilbert et al. 2007), these roads segments likely have
the greatest potential for high exposures directly connected to motor
vehicle emissions in the entire country. Typically, these very highly
trafficked roads are in the largest populated CBSAs, such as those with
2,500,000 people or more, and are somewhat atypical for CBSAs with less
than 2,500,000 people. As a result, EPA believes it is appropriate to
require a second monitor in a CBSA that has one or more road segments
with 250,000 AADT counts or more if they do not already have two near-
road monitors required due their population.
EPA received comments requesting that EPA explain the rationale for
the selection of the population thresholds that trigger minimum
monitoring requirements and also to reconsider the size of the network.
For example, NYDOT suggested that this final rule explain the basis for
the 350,000 and 2,500,000 population thresholds that will establish
near-road monitors. In another comment, the Clean Air Council (CAC)
questioned the selected population thresholds, noting that they believe
that the population thresholds that were proposed were too high.
Specifically, CAC stated that ``at 350,000 persons, numerous metro
areas in the mid-Atlantic and Northeastern States with urban cores and
highways running through will likely be exempted from the new
monitors.'' The Spokane Regional Clean Air Agency stated that they ``do
not believe it is necessary to require air quality monitoring for
NO2 near major roadways in every metropolitan area. It is
our [SRCAA's] view that EPA could establish a statistically significant
number of air quality monitoring stations near roadways and develop a
correlation between traffic density and ambient NO2
levels.'' Further, the EPA received many State comments suggesting
reductions to the overall size of the near-road network; however the
commenters did not provide very specific suggestions on how EPA should
accomplish that reduction in size. For example, the Regional Air
Pollution Control Agency, which represents a portion of Ohio, stated
``given the fairly standard fleet of vehicles on the nation's major
highways, we urge EPA to consider the need for 142 near-roadway
monitors. Perhaps a limited number of monitors across the country would
suffice to sufficiently characterize near-roadway NO2
levels.'' These State commenters provided various reasons which are
discussed throughout this document suggesting that the network be
reduced in size, including funding concerns (section III.B.1.b), the
perceived need to implement a smaller near-road research network in
lieu of a regulatory network (section III.B.1.b), safety issues
(section III.B.7.b), and problems with State implementation plans
(section VI. D) and designation issues (section V).
EPA notes that the intent of the first tier of the network design
is to support the revised NAAQS in measuring peak NO2
exposures in an area by including a minimum number of monitors
resulting in a sufficiently sized national near-road monitoring network
that will provide data from a geographically and spatially diverse
array of areas, in terms of population, potential fleet mixes,
geographic extent, and geographic setting, from across the country. The
U.S. Department of Transportation (U.S. DOT) Federal Highway
Administration (FHWA) ``Status of the Nation's Highways, Bridges, and
Transit: 2006 Conditions and Performance'' document (http://www.fhwa.dot.gov/policy/2006cpr/es02h.htm) states that ``while urban
mileage constitutes only 24.9 percent of total (U.S.) mileage, these
roads carried 64.1 percent of the 3 trillion vehicles miles (VMT)
travelled in the United States in 2004.'' The document also states that
``urban interstate highways made up only 0.4 percent of total (U.S.)
mileage but carried 15.5 percent of total VMT.'' These statements
indicate how much more traffic volume exists on roads in urban areas
versus the more rural areas that have significant amounts mileage of
the total public road inventory. The basis for the selection of the
proposed CBSA population level of 350,000 to trigger the requirement of
one near-road monitor was chosen in an attempt to provide near-road
monitoring data from a diverse array of areas, as noted above. However,
in response to the significant number of comments discussed above,
which in various ways encouraged at least a reduction of the size of
the required near-road network or the implementation of a relatively
smaller research network, EPA reconsidered the population threshold
that will require one near-road NO2 monitor in a CBSA.
EPA reviewed the data, such as population, geographic, and spatial
distribution, associated with particular CBSA areas that would and
would not be included in particular CBSA population thresholds.
According to the 2008 U.S. Census Bureau estimates (http://www.census.gov) there are 143 CBSAs with 350,000 or more persons
(including territories) which contain approximately 71% of the total
population (excluding territories). These
[[Page 6508]]
CBSAs collectively represent territory in 44 States, the District of
Columbia, and Puerto Rico. For comparison, there are 391 CBSAs with
100,000 or more persons, which contain approximately 86% of the total
population (excluding territories). These particular CBSAs collectively
represent territory in 49 States, the District of Columbia, and Puerto
Rico. Further, there are 102 CBSAs with 500,000 or more persons, which
contain approximately 66% of the total population (excluding
territories). These 102 CBSAs collectively represent territory in 43
States, the District of Columbia, and Puerto Rico. Finally, there are
22 CBSAs with 2,500,000 or more persons, which contain approximately
39% of the total population, collectively representing territory in 19
States, the District of Columbia, and Puerto Rico. In comparison to the
CBSA population threshold of 350,000, the 500,000 population threshold
has 41 less CBSAs. However, the percentage of the total U.S. population
residing in these two sets of CBSAs differs by only approximately 5
percent of the total population (e.g., 71% in CBSAs of 350,000 or more
versus 66% in CBSAs of 500,000 or more persons). Also, when comparing
the number of States that have some amount of their territory included
in these CBSAs, the difference between the two sets of CBSAs differs by
only 1 State (Alaska).
Further, EPA notes that the REA Air Quality Analysis, (REA, section
7.3.2) estimated the exceedences of health benchmark levels across the
United States, including explicit consideration of on- or near- roadway
exceedances in 17 urban areas associated with CBSA populations ranging
from approximately 19,000,000 to 540,000. The analysis indicated that
all 17 of the areas under explicit consideration were estimated to
experience NO2 concentrations on or near roads that exceeded
health benchmark levels.
c. Conclusions Regarding the First Tier (Near-Road Monitoring
Component) of the Network Design
After consideration of public comments, and in light of the
information discussed above, the Administrator has chosen to finalize
the CBSA population threshold for requiring a minimum of one near-road
monitor in CBSAs with a population of 500,000 or more persons. The
Administrator is finalizing the other thresholds that will trigger a
second near-road monitor as proposed. Accordingly, one near-road
NO2 monitor is required in CBSAs with a population greater
than or equal to 500,000 persons and a second near-road monitor is
required in CBSAs with a population greater than or equal to 2,500,000
persons, or in any CBSAs with one or more road segments with an Annual
Average Daily Traffic (AADT) count greater than or equal to 250,000.
The Administrator has concluded that using a population threshold
of 500,000 to require a minimum of one near-road monitor in a CBSA
provides a sufficiently sized, national network of near-road monitors
that will provide data from a geographically and spatially diverse set
of CBSAs that supports the intent of the revised NAAQS and continues to
meet the monitoring objectives of the network. Combined with the forty
additional monitors that the Regional Administrators are required to
site, discussed below, the monitoring network would cover an additional
percentage of the total population.
EPA believes that selecting a lower population threshold, such as
100,000 or, to a lesser degree, 350,000, as discussed in the above
examples, would create a much larger network of required near-road
monitors but would provide diminished population coverage per monitor,
compared to that provided by the 500,000 threshold. EPA notes that if a
particular area, such as one with a population less than 500,000
people, might warrant a near-road monitor, the Regional Administrator
has the authority to require additional monitors. The Regional
Administrators' authority is discussed in section III.B.4. Further,
States have the right to conduct additional monitoring above the
minimum requirements on their own initiative. In the Administrator's
judgment, selecting a higher threshold, such as 2,500,000, as was
suggested by some commenters, does not provide a sufficient
geographical and spatially diverse near-road network, compared to that
provided by the 500,000 threshold. The selection of the 2,500,000
population threshold to trigger a second near-road monitor, as noted
earlier in this section, is based on the fact that the larger urban
areas in the country are likely to have a greater number of major roads
across a potentially larger geographic area, and have a corresponding
increase in potential for population exposure to elevated levels in
different settings.
Changing the CBSA population threshold 350,000 to 500,000 results
in a near-road monitoring network requiring approximately 126 monitors
distributed within 102 CBSAs. Compared to the total number of required
near-road monitors that would have resulted from the proposed CBSA
population threshold of 350,000 (167 monitors), an estimated 41 fewer
monitors are required. EPA has also recognized that susceptible and
vulnerable populations, which include asthmatics and disproportionately
exposed groups, (as discussed in sections II.B.4 and II.F.4.d) are at
particular risk of NO2-related health effects. The
Administrator is therefore requiring the Regional Administrators,
working in collaboration with States, to site forty monitors in
appropriate locations, focusing primarily on protecting such
susceptible and vulnerable communities. This decision is discussed in
detail in section III.B.4.
3. Second Tier (Area-Wide Monitoring Component) of the Network Design
The following paragraphs provide background, rationale, and details
for the final changes to the second tier of the two-tier NO2
network design. In particular, this section will focus on the threshold
that triggers area-wide monitoring requirements. Area-wide site
selection and siting criteria details will be discussed in a subsequent
section.
a. Proposed Second Tier (Area-Wide Monitoring Component) of the Network
Design
As the second tier of the proposed two-tier network design, EPA
proposed to require monitors to characterize the expected maximum
NO2 concentrations at the neighborhood and larger (area-
wide) spatial scales in an area. This component of the two-tier network
design provides information on area-wide exposures that may occur due
to an individual or a group of point, area, on-road, and/or non-road
sources. Further, area-wide sites serve multiple monitoring objectives
aside from NAAQS comparison to both the 1-hour and the annual NAAQS,
including photochemical pollutant assessment, aiding in ozone
forecasting, aiding in particulate matter precursor analysis and
particulate matter forecasting. We proposed to require one area-wide
monitoring site in each CBSA with a population greater than or equal to
1,000,000. We proposed that these area-wide sites were to be sited to
represent an area of highest concentration at the neighborhood or
larger spatial scales. Based on 2008 Census Bureau statistics, there
are 52 CBSAs with 1,000,000 people or more, which would result in an
estimated 52 area-wide monitors in as many CBSAs being minimally
required. EPA also proposed to allow any current photochemical
assessment monitoring station (PAMS) sites that are sited where the
highest NO2 concentrations occur in an urban area
[[Page 6509]]
and represent a neighborhood or urban scale to satisfy the area-wide
monitoring requirement.
b. Comments
Most commenters who commented on area-wide monitoring supported the
adoption of the alternative area-wide network design and did not
specifically comment on the area-wide monitoring component of the
proposed two-tier network design. However, EPA did receive comments
from public health organizations on area-wide monitoring in the context
of the proposed network design. The public health group commenters,
including the ALA, EJ, EDF, and the NRDC, stated they ``oppose the
proposed requirement to retain only 52 air monitors to measure area-
wide concentrations of NO2.''
EPA understands the perceived concern to be that with this
provision, EPA is actively reducing the number of required area-wide
monitors. Prior to this rulemaking, the Ambient Air Monitoring
Regulations, 71 FR 61236 (Oct. 17, 2006) (2006 monitoring rule) removed
minimum monitoring requirements for NO2, and the rationale
for that action is explained in that rule; however, the 2006 Monitoring
rule has had a limited impact to date, evidenced by the fact that the
size of the NO2 network has remained relatively steady at
around 400 monitors, a majority of which are area-wide monitors, that
were operating in 2008 (Watkins and Thompson, 2008). The stability of
the NO2 network is due in large part to the fact that area-
wide monitors serve multiple monitoring objectives, including
photochemical pollutant assessment, pollutant forecasting, and in some
cases, support to ongoing health research. However, considering the
objective of this two-tier network design, particularly the first tier,
of supporting the revised NAAQS to protect against peak NO2
exposures, some shrinkage in the area-wide network is appropriate and
likely. EPA believes that the actual number of area-wide monitors that
will operate in the NO2 network will be greater than the
minimally required 52 sites, but likely less than the current number.
States and Regional Administrators will work together on which area-
wide sites may warrant retention above the minimum required if States
request existing area-wide sites to be shut down or relocated.
c. Conclusions on the Second Tier (Area-Wide Monitoring Component) of
the Network Design
Area-wide monitoring sites serve multiple monitoring objectives
aside from NAAQS comparison to both the 1-hour and the annual NAAQS,
including photochemical pollutant assessment, ozone forecasting,
particulate matter precursor analysis and particulate matter
forecasting. EPA recognizes that a significant portion of the existing
NO2 monitoring network can be characterized as area-wide
monitors and that these monitoring sites serve multiple monitoring
objectives, as noted above. In order to ensure that a minimum number of
area-wide monitors continue operating into the future, we are
finalizing the proposed minimum monitoring requirements for area-wide
monitors, where one area-wide monitor is required in any CBSA with
1,000,000 people or more. Since there were no adverse comments received
with regard to allowing PAMS stations that meet siting criteria to
satisfy minimum monitoring requirements for area-wide monitors, we are
finalizing that allowance as proposed. EPA encourages States to use the
upcoming 2010 network assessment process to review existing area-wide
NO2 sites to help determine what monitors might meet minimum
monitoring requirements and whether or not other existing monitors
warrant continued operation.
4. Regional Administrator Authority
The following paragraphs provide background, rationale, and details
for the final changes to Regional Administrator authority to use
discretion in requiring additional NO2 monitors beyond the
minimum network requirements. The proposed rule estimated that
approximately 167 near-road monitors would be required within CBSAs
having populations of 350,000 or more persons. As discussed above in
section III.B.2, in response to public comments, particularly from
States, EPA is changing the population threshold for siting a minimum
of one near-road NO2 monitor from CBSAs with 350,000 or more
persons to CBSAs with 500,000 or more persons. EPA estimates that this
change in the population threshold will result in a reduction in the
number of minimally required near-road NO2 monitors by
approximately forty monitors. EPA has also recognized that susceptible
and vulnerable populations, which include asthmatics and
disproportionately exposed groups (as discussed in sections II.B.4 and
II.F.4.d) are at particular risk of NO2-related health
effects. The Administrator is therefore requiring the Regional
Administrators, working in collaboration with States, to site these
forty monitors in appropriate locations, focusing primarily on
protecting susceptible and vulnerable communities. In addition, the
Regional Administrators, working with States, may take into account
other considerations described below in using their discretion to
require additional monitors.
a. Proposed Regional Administrator Authority
EPA proposed that Regional Administrators have the authority to
require monitoring at their discretion in particular instances. First,
EPA proposed that the Regional Administrator have discretion to require
monitoring above the minimum requirements as necessary to address
situations where the required near-road monitors do not represent a
location or locations where the expected maximum hourly NO2
concentrations exist in a CBSA. Second, EPA proposed to allow Regional
Administrators the discretion to require additional near-road
monitoring sites to address circumstances where minimum monitoring
requirements are not sufficient to meet monitoring objectives, such as
where exposures to NO2 concentrations vary across an area
because of varied fleet mixes, congestion patterns, terrain, or
geographic areas within a CBSA. And third, EPA proposed that Regional
Administrators have the discretion to require additional area-wide
NO2 monitoring sites above the minimum requirements for
area-wide monitors where the minimum requirements are not sufficient to
meet monitoring objectives.
b. Comments
EPA received comments from the Center on Race, Poverty and
Environment expressing concern that the proposed monitoring provisions
fail to consider ``disproportionately impacted communities'' which
include people of color and of lower socioeconomic status. The
commenter argues that this is ``a gaping hole'' in the proposed
monitoring system and disproportionately impacts minority and low
income populations in rural communities. In addition, the National
Tribal Air Association stated that ``Indian Tribes and Alaska Natives
are highly susceptible to health impacts as a result of NO2
exposure'' and ``the prevalence and severity of asthma is higher among
certain ethnic or racial groups such as Indian Tribes and Alaska
Natives,'' which is also discussed in section II.B.4 and the ISA (ISA,
section 4.4).
The proposed rule provided the Regional Administrators with the
authority to use their discretion and
[[Page 6510]]
consider certain factors to require monitors above the minimum number
in a CBSA. The proposal described one example where a Regional
Administrator might require an additional near-road monitor where ``a
particular community or neighborhood is significantly or uniquely
affected by road emissions.'' EPA recognizes that susceptible and
vulnerable populations, which include asthmatics and disproportionately
exposed groups, as noted in section II.F.4.d, are at particular risk of
NO2-related health effects, both because of increased
exposure and because these groups have a higher prevalence of asthma
and higher hospitalization rates for asthma. As noted above, in
conjunction with raising the threshold for requiring one near-road
NO2 monitor in CBSAs with 500,000 persons or more, EPA is
requiring the Regional Administrators, under their discretionary
authority, to work with States to site an additional forty monitors,
nationally, focusing primarily on communities where susceptible and
vulnerable populations are located. To address the risks of increased
exposure to these populations, the Administrator has determined that it
is appropriate and necessary, under this provision, to ensure these
additional forty monitors are sited primarily in communities where
susceptible and vulnerable populations are exposed to NO2
concentrations that have the potential to exceed the NAAQS (due to
emissions from motor vehicles, point sources, or area sources). As a
result of this action, the total number of monitors required through
this rulemaking is generally equivalent to the proposed number of
minimally required monitors.
EPA received comments from public health groups (e.g., ALA, Center
on Race, Poverty, and the Environment, EDF, EJ, NRDC) and the Swinomish
Tribe, who suggested that EPA expand monitoring coverage to address
impacts from stationary sources outside of urban areas. For example,
ALA, EDF, EJ, and NRDC, stated that ``EPA should require States and
local offices to review inventory data to identify any potential
NO2 hotspots outside of those large metropolitan areas. For
instance, if a large power plant or any other source is creating
elevated NO2 levels in proximity to homes, schools or other
sensitive sites, in an area of less than one million people, EPA should
consider requiring a monitor.''
EPA recognizes that there are major NO2 sources outside
of CBSAs that have the potential to contribute to NO2
concentrations approaching or exceeding the NAAQS. The issue is whether
such monitoring should be addressed through a more extensive set of
minimum requirements that might include monitoring near all large
stationary sources such as airports, seaports, and power plants, which
could lead to deploying a large number of monitors. EPA believes that a
more reasonable approach to address monitoring needs related to the
diverse set of point, area, and non-road mobile NO2 sources,
whether inside or outside of CBSAs, is to provide Regional
Administrators the authority to require additional monitoring in areas
where these impacts could occur. While the proposal did not
specifically state that Regional Administrators could require non-area-
wide monitors outside of CBSAs, EPA believes that it is important that
Regional Administrators have the authority to require NO2
monitoring in locations where NO2 concentrations may be
approaching or exceeding the NAAQS, whether located inside or outside
of CBSAs. Therefore, in the final rule, EPA is not limiting the
Regional Administrators' discretionary authority to require
NO2 monitoring only inside CBSAs; instead, the EPA is
providing Regional Administrators the authority to site monitors in
locations where NO2 concentrations may be approaching or
exceeding the NAAQS, both inside or outside of CBSAs.
The EPA also received comments from some State groups (e.g. the New
York Department of Environmental Conservation (NYSDEC), New York
Department of Transportation (NYSDOT), and the New York City Law
Department) and an industry group (the Council of Industrial Boiler
Operators) requesting greater clarification on the way in which
Regional Administrators may use their authority to require additional
monitors above the minimum requirements. For example, the Council of
Industrial Boiler Operators stated that ``this [Regional Administrator
authority] unreasonably vests an unbounded amount of discretion in EPA
to determine when ``minimum monitoring requirements are not
sufficient'' and which neighborhoods are ``uniquely affected,'' and
impose additional monitoring requirements where all applicable
monitoring requirements are already met by the State and local
agency.''
The authority of Regional Administrators to require additional
monitoring above the minimum required is not unique to NO2.
For example, Regional Administrators have or are proposed to have the
authority to use their discretion to require additional Pb monitors (40
CFR Part 58 Appendix D section 4.5), and have the discretion to work
with States or local agencies in designing and/or maintaining an
appropriate ozone network, per 40 CFR Part 58 Appendix D section 4.1.
EPA believes that while the NO2 monitoring network is
sufficiently sized and focused, a nationally applicable network design
may not account for all locations in which potentially high
concentrations approaching or exceeding the NAAQS exist. Therefore, EPA
believes it is important for Regional Administrators to have the
ability to address possible gaps in the minimally required monitoring
network, by granting them authority to require monitoring above the
minimum requirements.
One case in which the Regional Administrator may exercise
discretion in requiring a monitor might be a location or community
affected by a stationary source where the required near-road
NO2 monitor site is not the location of the maximum hourly
concentration in a CBSA. For any given CBSA, there is the possibility
that the maximum NO2 concentrations could be attributed to
impacts from one, or a combination of, multiple sources that could
include point, area, and non-road source emissions in addition to on-
road mobile source emissions. As a result, the Regional Administrator
may choose to require monitoring in such a location. In addition, there
is the possibility that a single source or group of sources exists
which may contribute to concentrations approaching or exceeding the
NAAQS at locations inside or outside CBSAs, including rural
communities. In such cases, Regional Administrators, working with
States, may require a monitor in these locations. Further, if there are
NO2 sources responsible for producing more widespread
impacts on a community or relatively larger area, Regional
Administrators may require an area-wide monitor to assess wider
population exposures, or to support other monitor objectives served by
area-wide monitors such as photochemical pollutant assessment or
pollutant forecasting.
Regional Administrators may also require additional monitoring
where a State or local agency is fulfilling its minimum monitoring
requirements with an appropriate number of near-road monitors, but an
additional location is identified where near-road population exposure
exists at concentrations approaching or exceeding the NAAQS. In this
case, the exposure may be due to differences in fleet mix, congestion
patterns, terrain, or geographic area, relative to any minimally
required monitoring site(s) in that area. We note
[[Page 6511]]
that such areas might exist in CBSAs with populations less than 500,000
persons.
EPA recognizes that high concentrations of NO2 that
approach or exceed the NAAQS could potentially occur in a variety of
locations in an area, and we believe that Regional Administrators
should have the discretion to require additional monitoring when a
location is identified based on the factors discussed in the paragraph
above. In such situations, State or EPA Regional staff is likely to
have identified these locations through data analysis, such as the
evaluation of existing ambient data and/or emissions data, or through
air quality modeling. Such information may indicate that an area has
NO2 concentrations that may approach or exceed the NAAQS,
and that there is potential for population exposure to those high
concentrations.
The Regional Administrator would use this authority in
collaboration with State agencies. We expect Regional Administrators to
work with State and local agencies to design and/or maintain the most
appropriate NO2 network to meet the needs of a given area.
For all the situations where a Regional Administrator may require
additional monitoring, including the forty additional monitors the
Regional Administrators are required to site, EPA expects Regional
Administrators to work on a case-by-case basis with States. Further,
for the forty additional monitors that will focus primarily on
protecting susceptible and vulnerable communities, EPA intends to work
with States to develop criteria to guide site selection for those
monitors.
c. Conclusions on Regional Administrator Authority
EPA is requiring Regional Administrators to work with States to
site forty NO2 monitors, above the minimum number required
in the two-tier network design, focused primarily in susceptible and
vulnerable communities exposed to NO2 concentrations that
have the potential to approach or exceed NAAQS. In addition,
recognizing that a nationally applicable monitoring network design will
not include all sites with potentially high concentrations due to
variations across locations, and in response to public comments, the
Administrator is providing Regional Administrators with the discretion
to require additional monitors above the minimum requirements.
Regional Administrators may also use their discretionary authority
to require monitoring above the minimum requirements as necessary to
address situations inside or outside of CBSAs in which (1) The required
near-road monitors do not represent all locations of expected maximum
hourly NO2 concentrations in an area and NO2
concentrations may be approaching or exceeding the NAAQS in that area;
(2) areas that are not required to have a monitor in accordance with
the monitoring requirements and NO2 concentrations may be
approaching or exceeding the NAAQS; or (3) the minimum monitoring
requirements for area-wide monitors are not sufficient to meet
monitoring objectives. In all cases in which a Regional Administrator
may consider the need for additional monitoring, EPA expects that
Regional Administrators will work with the State or local agencies to
evaluate evidence that suggests an area may warrant additional
monitoring. EPA also notes that if additional monitoring should be
required, as negotiated between the Regional Administrator and the
State, the State will modify the information in its Annual Monitoring
Network Plan to include any potential new sites prior to approval by
the EPA Regional Administrator.
5. Monitoring Network Implementation
The following paragraphs provide background, rationale, and details
for the final changes to the approach for the monitoring network
implementation.
a. Proposed Monitoring Network Implementation Approach
EPA proposed that State and, when appropriate, local air monitoring
agencies provide a plan for deploying monitors in accordance with the
proposed network design by July 1, 2011. EPA also proposed that the
proposed NO2 network be physically established no later than
January 1, 2013.
b. Comments
Most environmental and public health group commenters suggested
that EPA change the implementation date from the proposed January 1,
2013 to a date that would require the minimum required NO2
network to be deployed sooner than proposed. Most States and State
group commenters, along with industry group commenters, recommended
that EPA keep the network implementation date as January 1, 2013, or
move it later than proposed. Those commenters who suggested moving it
later noted that issues with monitoring site identification, site
development, and overall lack of experience working in the near-road
environment would make implementation difficult under the proposed
implementation deadline.
EPA recognizes the challenges involved with deploying the two-tier
network design by the January 1, 2013 date. We recognize the need for
additional information and plan to aid State agencies in the network
implementation process, particularly by developing guidance in
partnership with affected stakeholders, ideally including at a minimum
NACAA and the States. EPA agrees with NACAA's suggestion that the CASAC
Ambient Air Monitoring and Methods subcommittee should be consulted as
part of developing any guidance developed for near-road monitoring, and
has already begun the process by scheduling meetings with them
regarding near-road monitoring. Further, EPA believes that
collaboration with the States and State groups in developing guidance
will be highly beneficial to the implementation process. This would
allow for those States that do have increased experience in near-road
monitoring to support the guidance development process and provide a
conduit for sharing experiences amongst all stakeholders.
In perspective, EPA believes that the approximate 2 years and 11
months between promulgation of this rulemaking and the mandated January
1, 2013 network implementation date includes extra time relative to
what is traditionally allowed for network implementation following
rulemakings. We are also cognizant of the time needed to collect
complete data that would allow data from the two-tier network to be
considered for designations and for use in the next NO2
NAAQS review data from the 2013, 2014, and 2015 years would provide
critical information in the next NAAQS review, intended to occur on a
5-year cycle, and for use in subsequent designations. Even with
complete data from 2013, 2014, and 2015 years designations would not
occur until 2017, at the earliest.
c. Conclusions on Monitoring Network Implementation
EPA is finalizing the date by which State and, when appropriate,
local air monitoring agencies shall establish the required
NO2 monitoring network as January 1, 2013, as was proposed.
We believe that the allotted time for implementation will allow for the
development of guidance documentation, particularly allowing for
interactions with CASAC and NACAA/States, and for the processes that
will be involved in deploying this network. However, EPA recognizes
that the network implementation process,
[[Page 6512]]
particularly for near-road monitors, will include the assessment of
road segments in CBSAs to identify locations of maximum expected hourly
NO2 concentrations, identifying and working with other State
and local agencies, such as transportation officials, as needed on
issues regarding access and safety, and the exchange of information and
feedback on potential sites with EPA, prior to any commitment to
selecting and presenting new sites in an annual monitoring plan. As a
result, based on feedback received through public comments, and to
allow for more time to process guidance information, to carry out the
deployment processes, and to allow for information exchanges to occur,
we are changing the date by which State and, when appropriate, local
air monitoring agencies shall provide a plan for deploying monitors in
accordance with required network design, including the monitors
required under the Regional Administrators' discretional authority
which are to be primarily focused on providing protection to
susceptible and vulnerable populations, as discussed in section
III.B.4, from July 1, 2011 to July 1, 2012. EPA strongly encourages
State and local air agencies to supply as much information as possible
on the NO2 sites they may be considering, including possible
site coordinates if available, or have possibly selected, to satisfy
the minimum NO2 network monitoring requirements in their
Annual Monitoring Network Plan submitted July 1, 2011.
6. Near-Road Site Selection
The following paragraphs provide background, rationale, and details
for the final changes to the approach and criteria by which required
near-road sites shall be selected.
a. Proposed Near-Road Site Selection Criterion
EPA proposed that the required near-road NO2 monitoring
stations shall be selected by ranking all road segments within a CBSA
by AADT and then identifying a location or locations adjacent to those
highest ranked road segments where maximum hourly NO2
concentrations are expected to be highest and siting criteria can be
met in accordance with that proposed for 40 CFR Part 58 Appendix E
(discussed in III.B.7). Where a State or local air monitoring agency
identifies multiple acceptable candidate sites where maximum hourly
NO2 concentrations are expected to occur, the monitoring
agency should consider taking into account the potential for population
exposure in the criteria utilized to select the final site location.
Where one CBSA is required to have two near-road NO2
monitoring stations, we proposed that the sites shall be differentiated
from each other by one or more of the following factors: Fleet mix;
congestion patterns; terrain; geographic area within the CBSA; or
different route, interstate, or freeway designation.
b. Comments
EPA received many comments from CASAC, public health groups, States
and State groups, and industry groups on the proposed process by which
States will select near-road sites. CASAC, along with some health group
and State commenters questioned how States should select a site near
the road with the highest ranked AADT possible, noting that EPA did not
appear to require States to account for other factors. For example, one
CASAC panel member noted that siting monitors based on traffic counts
alone might miss locations where maximum NO2 concentrations
would occur. They proceeded to recommend the use of modeling to assist
in the site selection process. In another example, the ALA, EDJ, EJ,
and NRDC, stated that ``Near-road monitor placement should be
determined not only by the highest AADT volumes in a given CBSA, but
also by the highest heavy-duty truck volumes.'' NACAA also expressed
concerns on ``* * * basing monitor locations on the annual average
daily traffic (AADT) without regard to vehicle mix or dispersion
characteristics * * *''.
EPA does not intend for AADT counts to be the sole basis for
choosing a near-road site. As noted earlier in section III.B.2, there
is a general relationship between AADT and mobile source pollution,
where higher traffic counts correspond to higher mobile source
emissions. The use of AADT counts is intended to be a mechanism for
focusing on identifying the locations of expected maximum
NO2 concentrations due to mobile sources. There are other
factors that can influence which road segment in a CBSA may be the
actual location where the maximum NO2 concentrations could
occur. These factors include vehicle fleet mix, roadway design,
congestion patterns, terrain, and meteorology. When States identify
their top-ranked road segments by AADT, EPA intends for States to
evaluate all of the factors listed above in their site selection
process, due to their influence on where the location of expected
maximum NO2 concentration may occur. As a result of the
comments indicating a need for clarification, EPA will specifically
list the factors that must be considered by States in their site
selection process once a State has identified the most heavily
trafficked roads in a CBSA based on AADT counts. In addition, EPA
proposed that States consider these factors when they are required to
place two near-road monitors in a CBSA, i.e., CBSAs with a population
of 2,500,000 persons or more. EPA notes that these factors will be used
in differentiating the two monitoring sites from each other, providing
further characterization of near-road environments in larger urban
areas that are more likely to have a greater number of major roads
across a potentially larger geographic area, and a corresponding
increase in potential for exposure in different settings. Finally, EPA
notes that air quality models, which were noted by the CASAC panel
member to be considered for use in near-road site selection, are tools
that EPA believes will be useful, and likely used by some States to
inform where near-road sites need to be placed.
EPA received comments from some State and industry commenters (e.g.
Iowa, NY DEC, Edison Electric Institute, and Savannah River Nuclear
Solutions) who suggested that potential population exposure should be a
first-level metric in the near-road monitoring site selection process,
instead of a second-level metric as EPA had proposed.
EPA notes that the intent of the revised primary NO2
NAAQS is to protect against the maximum allowable NO2
concentration anywhere in an area, which includes ambient air on and
around roads. This would limit exposures to peak NO2
concentrations, including those due to mobile source emissions, across
locations (including those locations where population exposure near
roads is greatest) in a given CBSA or area, with a relatively high
degree of confidence. We also note the agency's historical practice has
been to site ambient air monitors in locations of maximum
concentration, at the appropriate spatial scale. If EPA were to allow
population, population density, or another population weighted metric
to be a primary factor in the decision on where required near-road
NO2 monitors are to be located, it is possible that the
required near-road monitors in a CBSA would not be located at a site of
expected maximum hourly near-road NO2 concentration. By
monitoring in the location of expected maximum 1-hour concentrations,
near-road monitoring sites will likely represent the highest
NO2 concentrations in an area directly attributable to
mobile sources or a group of sources that includes mobile sources. The
proposed rule did permit, and the final rule states, that States are to
[[Page 6513]]
consider population in the site selection process in situations when a
State identifies multiple candidate sites where maximum hourly
NO2 concentrations are expected to occur.
EPA received a comment from HCPHES suggesting that required
monitoring should take into consideration the location of other major
mobile sources for NO2 emissions such as airports and
seaports. EPA also received a comment from the South Carolina
Department of Health and Environmental Control stating that a near-road
network does not address ``widespread pollutants from numerous and
diverse sources.''
EPA recognizes that there are major NO2 sources outside
of CBSAs that have the potential to contribute to NO2
concentrations approaching or exceeding the NAAQS. The issue is whether
such monitoring should be addressed through a more extensive set of
minimum requirements that might include monitoring near all large
stationary sources such as airports, seaports, and power plants, which
could lead to deploying a large number of monitors. EPA believes that a
more reasonable approach to address monitoring needs related to the
diverse set of point, area, and non-road mobile NO2 sources,
whether inside or outside of CBSAs, is to provide Regional
Administrators the authority to require additional monitoring in areas
where these impacts could occur. Providing the Regional Administrators
with the discretion to require additional monitors allows them to
effectively address such situations, even if that area is satisfying
minimum monitoring requirements. This Regional Administrator authority
is discussed above in section III.B.4. EPA also notes that State and
local agencies may also monitor such locations on their own initiative.
One State commenter, the Wisconsin Department of Natural Resources,
requested that the term ``major road'' be defined and also requested
clarification on what ``top-ranked'' means with regard to AADT counts
on road segments. While the term ``major road'' is widely used in
literature and can be found to be defined differently from one
scientific study to another, here, EPA is using it in its commonly
understood meaning as a road that is relatively heavily trafficked. EPA
also does not believe it is appropriate to provide a bright-line
definition for ``top-ranked''. Each CBSA will have a different
distribution of total road segments and corresponding AADT counts on
those segments. Further, since required near-road monitors are to be
sited in locations of expected maximum concentrations, a percentile
restriction on ``top ranked'' roads is unnecessary. The intent of the
requirement to rank all road segments by AADT counts and select a site,
considering the other local factors noted above, near a ``top-ranked''
road segment is to focus attention on the most heavily trafficked
roads, around which there is higher potential for maximum
NO2 concentrations to occur.
c. Conclusions on Near-Road Site Selection
We are finalizing the near-road site selection criteria as
proposed, and are clarifying that the proposal intended the selection
criteria to include consideration of localized factors when identifying
locations of expected maximum concentrations. As a result, required
near-road NO2 monitoring stations shall be selected by
ranking all road segments within a CBSA by AADT and then identifying a
location or locations adjacent to those highest ranked road segments,
considering fleet mix, roadway design, congestion patterns, terrain,
and meteorology, where maximum hourly NO2 concentrations are
expected to occur and siting criteria can be met in accordance with 40
CFR Part 58 Appendix E. As was noted in section III.B.5 above, EPA will
work with States to assist with the near-road site selection process
through the development of guidance material and through information
exchanges amongst the air monitoring community.
We are also finalizing the requirement, as proposed, that when one
CBSA is required to have two near-road NO2 monitoring
stations, the sites shall be differentiated from each other by one or
more of the following factors: fleet mix; congestion patterns; terrain;
geographic area within the CBSA; or different route, interstate, or
freeway designation, as was proposed.
7. Near-Road Siting Criteria
The following paragraphs provide background, rationale, and details
for the final changes to the siting criteria for required near-road
monitoring sites.
a. Proposed Near-Road Siting Criteria
EPA proposed that near-road NO2 monitoring stations must
be sited so that the NO2 monitor probe is no greater than 50
meters away, horizontally, from the outside nearest edge of the traffic
lanes of the target road segment, and shall have no obstructions in the
fetch between the monitor probe and roadway traffic such as noise
barriers or vegetation higher than the monitor probe height. We
solicited comment on, but did not propose, having near-road sites
located on the predominantly downwind side of the target roadways. EPA
proposed that the monitor probe shall be located within 2 to 7 meters
above the ground, as is required for microscale PM2.5 and
PM10 sites. We also proposed that monitor probe placement on
noise barriers or buildings, where the inlet probe height is no less
than 2 meters and no more than 7 meters above the target road, will be
acceptable, so long as the inlet probe is at least 1 meter vertically
or horizontally away (in the direction of the target road) from any
supporting wall or structure, and the subsequent residence time of the
pollutant in the sample line between the inlet probe and the analyzer
does not exceed 20 seconds.
b. Comments
EPA received comments from a number of States (e.g. Michigan,
Mississippi, and Tennessee) indicating that the near-road network poses
significant safety issues and a related need for increased logistical
flexibility for installing a monitoring site. For example, the
Mississippi Department of Environmental Quality states that ``Given the
fact that these NO2 sites will be required to be housed in
shelters that are within 50 meters of the road, we believe that these
buildings could be large and pose a serious risk to drivers on the
road.''
EPA notes that in all instances of field work, safety is a top
priority. In this instance of near-road monitoring, we are dealing with
the safety of the public driving on roads and the monitoring staff who
may operate the near-road monitoring station as well. There are various
ways to install near-road sites while ensuring worker and traffic
safety, and safety is an important part of the logistical
considerations that States should consider when selecting and
installing near-road sites. In many cases, State and local monitoring
agencies may be able to work with their State or local transportation
officials during the site selection process to deal with access and
safety issues. In public comments, AASHTO recommended that ``* * *
State and local air monitoring agencies be required to coordinate with
State and local DOTs for near-road monitoring during the establishment
of the monitoring plan.'' Although EPA cannot require States to
coordinate with other State or local entities, EPA believes that
transportation officials would likely be able to assist in finding
solutions to ensure safety while working with monitoring agencies in
accommodating a new near-road monitoring station. An
[[Page 6514]]
example of a step that could be taken to alleviate safety concerns
might be purposefully placing a monitoring site behind existing
barriers like guardrails and fencing, or possibly by installing a short
distance of such barriers to protect the site workers, site
infrastructure, and nearby traffic. In addition, EPA notes that the 50m
distance proposed is wide enough to accommodate a site that would
satisfy many setback provisions that exist for private or commercial
building permits near roads, and may be viewed as a confirmation that
our proposed siting criteria are safely attainable.
Some State commenters (e.g. AASHTO, NYSDOT, and Wisconsin)
suggested that the allowable maximum distance a near-road monitoring
probe can be from the target road be increased from 50 meters to
something wider, such as 200 meters. Conversely, there were some State,
environmental, and industry commenters (e.g. NESCAUM,\24\ Group Against
Smog and Pollution, and Air Quality Research and Logistics) who
suggested that the proposed range was appropriate, or, as suggested by
both NESCAUM and the Group Against Smog and Pollution, the allowable
distance should be reduced to as close as 30 or 20 meters to the
nearest edge of the traffic lanes of the target road segment,
respectively.
---------------------------------------------------------------------------
\24\ NESCAUM officially supported the alternative network
design; however, they made suggestions regarding the near-road
network in the event EPA finalized the proposed two-tier network
design.
---------------------------------------------------------------------------
EPA believes that increasing the allowable distance above 50 meters
would compromise the intent of near-road monitoring. As was noted in
the proposal and this document, the ISA (2.5.4 and 4.3.6) and REA
(7.3.2) indicate that on-road, mobile source derived NO2
exhibits a peak concentration on or very near the source road, and
those concentrations decay over a variable but relatively short
distance back to near area-wide or background (upwind of the target
road) concentrations. Literature values indicate that the distance
required for NO2 concentrations to return to near area-wide
or background concentrations away from major roadways can range up to
500 meters, but the peak concentrations are occurring on or very near
the source roadway. The behavior of NO2 concentrations and
the actual distance over which concentrations return to near area-wide
or background levels is variable, and highly dependent on topography,
roadside features, meteorology, and the related photochemical
reactivity conditions (Baldauf et al., 2008; Beckerman et al., 2007;
Clements et al., 2008; Gilbert et al., 2003; Hagler et al., 2009; Rodes
and Holland, 1980; Singer et al., 2003; Zhou and Levy, 2007).
Therefore, monitor probe placement at increasing distances from a road,
such as 200 meters, will correspondingly decrease the potential for
sampling maximum concentrations of NO2 due to the traffic on
the target road. Baldauf et al. (2009) indicate that monitoring probes
would ideally be situated between 10 and 20 meters from the nearest
traffic lane for near-road pollutant monitoring.
Regarding the comments suggesting required monitor probes be closer
than 50 meters, EPA believes the allowable distance of 50 meters that a
near-road NO2 probe can be from the target road provides
enough flexibility for the logistical issues that can occur on a case-
by-case basis, which is inherent in monitoring site placement, while
not sacrificing the potential to monitor the peak NO2
concentrations. However, in light of the information provided here on
how NO2 peak concentrations can decay over relatively short
distances away from roads, EPA strongly encourages States to place
near-road sites, or at least monitor probes, as close as safely
possible to target roads to increase the probability of measuring the
peak NO2 concentrations that occur in the near-road
environment, again noting that Baldauf et al. (2009) indicate that
monitor probes would ideally be situated between 10 and 20 meters from
the nearest traffic lane for near-road pollutant monitoring.
EPA also proposed that required near-road NO2 monitor
probes shall have no obstructions in the fetch between the monitor
probe and roadway traffic such as noise barriers or vegetation higher
than the monitor probe height. EPA expects that when a State makes a
measurement in determining whether an NO2 inlet probe is no
greater than 50 meters away, horizontally, from the outside nearest
edge of the traffic lanes of the target road segment, that the
measurement would likely represent a path to the monitor probe that is
normal to the target road. However, EPA notes that the monitor probe
will likely be influenced by various parts of the target road segment
that are at a relative angle compared to the normal transect between
the road and the monitor probe. EPA is not adjusting the wording of
this requirement, but does intend for States to consider more than one
linear pathway between the target road and the monitor probe being
clear of obstructions when considering candidate site locations.
EPA received comments on the solicitation for comment on requiring
near-road monitoring sites to be placed on the downwind side of the
target road where the commenters (e.g. NACAA,\25\ NESCAUM, and the
Clean Air Council) encouraged such a requirement. Conversely, other
commenters (e.g., Air Quality and Logistics and NYSDEC suggested that
such a requirement may be overly restrictive and not necessary. For
example, NYSDEC stated that ``It is important to avoid making the
monitor siting criteria too restrictive. It is very likely that in some
CBSAs, finding suitable locations near the busiest road segments will
not be possible. It is also important to remember that the
NO2 monitoring instrumentation provides data continuously.
Sites located downwind of sources will likely be impacted more
frequently than the sites located upwind particularly when the sites
are more than 50 meters from the source, and are preferred, but either
side of the road will be downwind some of the time. Many of the highest
NO2 concentrations are also likely to occur during inversion
periods and during calm meteorological conditions when the upwind-
downwind designations have little meaning.''
---------------------------------------------------------------------------
\25\ NACAA made a statement containing many concerns about the
near-road monitoring component proposal which included a passage
regarding the lack of requiring sites to be downwind. They expressed
concern in ``* * * allowing upwind siting of monitors over a wide
range of horizontal and vertical distances from the road * * *''.
---------------------------------------------------------------------------
EPA noted in its proposal that research literature indicates that
in certain cases, mobile source derived pollutant concentrations,
including NO2, can be detected upwind of roads, above
background levels, due to a phenomenon called upwind meandering.
Kalthoff et al. (2007) indicates that mobile source derived pollutants
can meander upwind on the order of tens of meters, mainly due to
vehicle induced turbulence. Further, Beckerman et al. (2008) note that
near-road pollutant concentrations on the predominantly upwind side of
their study sites dropped off to near background levels within the
first 50 meters, but were above background in this short and variable
upwind range, which could be due, at least in part, to vehicle induced
turbulence. This upwind meandering characteristic of pollutants in the
near-road environment provides an additional basis for locating near-
road sites within 50 meters of target road segments, but also reduces
the absolute need to be downwind of the road. EPA believes that very
few, if any, near-road sites would be able to be situated in a location
that was always downwind. For example, a hypothetical
[[Page 6515]]
site may have winds routinely out of several different cardinal
directions throughout the year, without one being a dominant direction.
As a result, given variable meteorology, for some period of a year, a
given near-road site may not be downwind of the target road, no matter
which side of the road it is on. Therefore, EPA is not finalizing a
requirement that near-road sites must be climatologically downwind of
the target road segment because of the additional limitations this
introduces to finding potential site candidates in exchange for what
may be a small increase in the opportunity to monitor peak
NO2 concentrations. However, EPA encourages States to place
monitors in the climatologically downwind direction whenever possible,
in an attempt to measure the peak NO2 concentrations more
often than not. One way States may identify where the predominantly
downwind location might be for candidate sites could be to use portable
meteorological devices to characterize meteorological tendencies, in
addition to evaluating other available meteorological data sources.
EPA proposed that required near-road NO2 monitor probes
be located within 2 to 7 meters above the ground, as is required for
microscale PM2.5 and PM10 sites. EPA also
proposed that monitor probe placement on noise barriers or buildings,
where the inlet probe height is no less than 2 meters and no more than
7 meters above the target road, will be acceptable, so long as the
inlet probe is at least 1 meter vertically or horizontally away (in the
direction of the target road) from any supporting wall or structure.
NESCAUM commented that ``EPA needs to reconcile near-roadway
NO2 probe height requirements with the existing micro-scale
near-roadway CO probe height requirement of 2.5 to 3.5 meters above
prevailing terrain. NESCAUM supports using this existing height for all
near-roadway pollution monitors, as it minimizes probe height effects
on measurements, and allows for proper measurement of collocated
particle number concentration (which requires a very short inlet, i.e.,
on the order of inches) and CO.'' NYSDEC commented that ``The height
requirement may not be practical for road segments in dense urban areas
where existing buildings heights may exceed 7 meters. The requirement
to maintain a 1 meter clearance from a supporting wall or structure may
not be adequate for taller walls often found in urban areas. These
walls can create down washing and street canyon effects which will make
the resulting data less representative of nearby areas and will make
interpretation of the resulting data difficult. However, there will
need to be consistency between similar site settings.'' Finally, EPA
received comments from some health groups (e.g., ALA, EJ, EDF, and
NRDC) who commented that ``the lower end of the proposed height of 2 to
7 meters appears to capture the highest NO2 concentrations,
and more accurately represents human exposure at the breathing zone.''
In the proposal, EPA noted that near-road monitoring sites will be
adjacent to a variety of road types, where some target roads will be on
an even plane with the monitoring station, while others may be cut
roads (i.e., below the plane of the monitoring station) or fill and
open elevated roads (i.e., where the road plane is above the monitoring
station). EPA recognizes that consistency across sites with regard to
probe height is desirable, and consistency with microscale, urban
canyon CO sites might also be desirable. However, as was noted in the
earlier discussion on ``downwind'' site placements, it is important to
avoid making the monitor siting criteria too restrictive. An allowable
range between 2 and 7 meters provides more flexibility in site
installation, which EPA considers important because of the variety of
siting situations each State may have to deal with for each individual
site. While EPA agrees that a tighter allowable range such as 2.5 to
3.5 meters would reduce site to site variability and keep probes nearer
the microscale siting requirements of CO, the wider range of 2 to 7
meters still provides an adequate amount of site to site consistency.
EPA may also address this issue through forthcoming guidance, where an
increased consistency for probe heights in similar situations such as
urban canyons may be a site implementation goal, within the required 2
to 7 meter probe height range. Further, EPA believes that although
certain situations, as noted by NYSDEC, may exist where the 1 meter
clearance from walls or structures may be problematic near taller
buildings or walls, this requirement is consistent with similar such
clearance requirements for microscale CO sites in similar such
situations that exist in urban canyons.
In the proposed rule, EPA proposed in the siting criteria language
that the subsequent residence time of the pollutant in the sample line
between the inlet probe and the analyzer cannot exceed 20 seconds. EPA
received comments from Air Quality Research and Logistics regarding
guidelines for maximum allowable inlet length and sample residence
time, where they stated that ``* * * the fast photodynamic
O3-NOX equilibrium may occur in darkened sample
lines at residence times of 10-20 seconds (Butcher et al. 1971; Ridley
et al. 1988; Parrish et al. 1990). EPA should correct this apparent
error by specifying much lower maximum residence times (e.g., 1-2
seconds) or accounting for this effect by reporting `corrected' values
in error by no more than the allowed rounding convention (e.g., 1 ppb).''
EPA notes that in 40 CFR Part 58 Appendix E, paragraph (9)(c),
states that sample probes for reactive gas analyzers, particularly
NOY monitors, at NCore monitoring sites must have a sample
residence time less than 20 seconds. EPA believes this rule is also
appropriate for NO2 monitors, particularly if a monitor
inlet manifold is extended away from the main monitoring shelter. EPA
does agree that shorter sample residence time in the inlet manifold is
desirable. Although we do not believe it appropriate to require
residence times on the order of 1 to 2 seconds, and do not believe
correcting values is appropriate (which was not a concept which was
proposed), we do encourage States to use best practices in selecting
non-reactive manifold materials, and to install sampling manifolds in
an efficient manner that minimizes sample residence time. While EPA
proposed this concept in the preamble to the proposed rule, we did not
include it in the proposed regulatory text. The final rule includes
regulatory text on this subject at 40 CFR Part 58 Appendix E, paragraph
(9)(c).
c. Conclusions on Near-Road Siting Criteria
We are finalizing the near-road NO2 monitor siting
criteria, as proposed, where (1) required near-road NO2
monitor probes shall be as near as practicable to the outside nearest
edge of the traffic lanes of the target road segment; but shall not be
located at a distance greater than 50 meters, in the horizontal, from
the outside nearest edge of the traffic lanes of the target road
segment, (2) required near-road NO2 monitor probes shall
have an unobstructed air flow, where no obstacles exist at or above the
height of the monitor probe, between the monitor probe and the outside
nearest edge of the traffic lanes of the target road segment, (3)
required near-road NO2 monitors are required to have sampler
inlets between 2 and 7 meters above ground level, and (4) residence
time of NO2 in the sample line between the
[[Page 6516]]
inlet probe and the analyzer does not exceed 20 seconds.
8. Area-Wide Monitor Site Selection and Siting Criteria
The following paragraphs provide background, rationale, and details
for the final changes to the site selection and monitor siting criteria
for required area-wide monitoring sites.
a. Proposed Area-Wide Monitor Site Selection and Siting Criteria
EPA proposed that sites required as part of the second tier of the
NO2 monitoring network design, known as the area-wide
monitoring component, be sited to characterize the highest expected
NO2 concentrations at the neighborhood and larger (area-
wide) spatial scales in a CBSA.
b. Comments
While most commenters who supported area-wide monitoring did so
with regard to the adoption of the alternative area-wide network design
rather than as part of the proposed approach, only a few commented on
the actual sites and siting criteria. The Dow Chemical Company
suggested that area-wide sites should be located at least 1,000 meters
away from any major roads or intersections to ensure that the
concentration of NO2 measured is representative of an area-
wide concentration instead of peak near-road concentrations.
EPA notes that in order for an NO2 monitoring site to be
classified as a neighborhood (or larger) spatial scale site, it must
meet the roadway set-back requirements in Table E-1 of 40 CFR Part 58
Appendix E. EPA believes that this existing set-back table is
appropriate to use to ensure that any NO2 site that may be
intended as an area-wide site will be sufficiently distanced from any
major road. For example, an NO2 monitoring site may be
considered neighborhood scale if it is 10 or more meters from the edge
of the nearest traffic lane of a road with 10,000 or less AADT counts.
c. Conclusions on Area-Wide Monitor Site Selection and Siting Criteria
We are finalizing the requirement that any sites required as part
of the second tier of the NO2 monitoring network design,
known as the area-wide monitoring component, be sited to characterize
the highest expected NO2 concentrations at the neighborhood
and larger (area-wide) spatial scales in a CBSA.
9. Meteorological Measurements
The following paragraphs provide background, rationale, and details
for the final changes to the requirement of meteorological monitoring
at near-road monitoring sites.
a. Proposed Meteorological Measurements
In further support of characterizing the peak NO2
concentrations occurring in the near-road environment, EPA proposed to
require three-dimensional anemometry, providing wind vector data in the
horizontal and vertical planes, along with temperature and relative
humidity measurements, at all required near-road monitoring sites.
b. Comments
EPA received comments from the South Carolina Department of Health
and Environmental Control commented that the recording of air
turbulence data at near-road monitoring stations should be encouraged
but not required. Other States (e.g., Alaska, North Carolina, and
Wisconsin) provided comments that did not support the proposed
meteorological measurement requirements, noting issues with costs,
problems siting the probe nearer to structures and to the ground than
is typically done, and that the averaging period required to better
understand turbulence (through anemometry data) in the near-road
environment requires a much higher frequency than what is typically
reported.
EPA is removing the proposed requirements that would have required
meteorological monitoring at near-road NO2 monitoring
stations. However, EPA strongly encourages States to do some
meteorological monitoring to better characterize the conditions under
which they are acquiring NO2 data. The near-road microscale
environment is complex, and understanding the turbulent dispersion that
may be affecting NO2 measurements, along with having a basic
understanding of from which direction the measured NO2
concentrations are coming from, which are very informative in the
effort to fully understand the data being collected. At a minimum,
basic anemometry data would be useful in identifying whether the site
is upwind, downwind, or otherwise oriented, relative to the target
road.
c. Conclusions on Meteorological Measurements
We are not finalizing the proposal to require three-dimensional
anemometry, providing wind vector data in the horizontal and vertical
planes, along with temperature and relative humidity measurements, at
all required near-road monitoring sites.
C. Data Reporting
The following paragraphs provide background, rationale, and details
for the final changes to the data reporting requirements, data quality
objectives, and measurement uncertainty.
1. Proposed Data Quality Objectives and Measurement Uncertainty
In the proposal, EPA noted that State and local monitoring agencies
are required to report hourly NO, NO2, and NOX
data to AQS within 90 days of the end of each calendar quarter. We also
noted that many agencies also voluntarily report their pre-validated
data on an hourly basis to EPA's real time AIRNow data system, where
the data may be used by air quality forecasters to assist in ozone
forecasting. We believe these data reporting procedures are appropriate
to support the revised primary NO2 NAAQS.
EPA proposed to develop data quality objectives (DQOs) for the
proposed NO2 network. We proposed a goal for acceptable
measurement uncertainty for NO2 methods to be defined for
precision as an upper 90 percent confidence limit for the coefficient
of variation (CV) of 15 percent and for bias as an upper 95 percent
confidence limit for the absolute bias of 15 percent.
2. Comments
EPA received comments from the State of Missouri, supporting the
proposed DQOs and goals for measurement uncertainty, and from North
Carolina, suggesting that measurement uncertainty goals match those of
the NCore multi-pollutant network.
EPA agrees that it is desirable to have measurement uncertainty
goals that match that of other pollutants. EPA originally proposed the
goals for precision and bias under consideration that there may be a
need to account for potential increased uncertainty in 1-hour near-road
NO2 data. However, we agree with the suggestion from the
State of North Carolina, and are changing the goals for acceptable
measurement uncertainty for NO2 methods to be defined for
precision as an upper 90 percent confidence limit for the coefficient
of variation (CV) of 10 percent and for bias as an upper 95 percent
confidence limit for the absolute bias of 15 percent. These goals match
the existing goals for NO2 and are consistent with
historical measurement uncertainty goals.
[[Page 6517]]
3. Conclusions on Data Quality Objectives and Measurement Uncertainty
We are finalizing the approach to develop data quality objectives,
and are changing the proposed goal for measurement uncertainty, where
the goals for acceptable measurement uncertainty for NO2
methods to be defined for precision as an upper 90 percent confidence
limit for the coefficient of variation (CV) of 10 percent and for bias
as an upper 95 percent confidence limit for the absolute bias of 15
percent.
IV. Appendix S--Interpretation of the Primary NAAQS for Oxides of
Nitrogen and Revisions to the Exceptional Events Rule
The EPA proposed to add Appendix S, Interpretation of the Primary
National Ambient Air Quality Standards for Oxides of Nitrogen, to 40
CFR part 50 in order to provide data handling procedures for the
proposed NO2 1-hour primary standard and for the existing
NO2 annual primary standard. The proposed Appendix S
detailed the computations necessary for determining when the proposed
1-hour and existing annual primary NO2 NAAQS are met. The
proposed Appendix S also addressed data reporting, data completeness
considerations, and rounding conventions.
Two versions of Appendix S were proposed. The first applied to a 1-
hour primary standard based on the annual 4th high value form, while
the second applied to a 1-hour primary standard based on the 99th
percentile daily value form.
The final version of Appendix S is printed at the end of this
notice and applies to an annual primary standard and a 1-hour primary
standard based on the 98th percentile daily value form. Appendix S is
based on the near-roadway approach to the setting the level of the 1-
hour standard and to siting monitors. As such, these versions place no
geographical restrictions on which monitoring sites' concentration data
can and will be compared to the 1-hour standard when making
nonattainment determinations and other findings related to attainment
or violation of the standard.
The EPA is amending and moving the provisions of 40 CFR 50.11
related to data completeness for the existing annual primary standard
to the new Appendix S, and adding provisions for the proposed 1-hour
primary standard. Substantively, the data handling procedures for the
annual primary standard in Appendix S are the same as the existing
provisions in 40 CFR 50.11 for that standard, except for an addition of
a cross-reference to the Exceptional Events Rule, the addition of
Administrator discretion to consider otherwise incomplete data
complete, and the addition of a provision addressing the possibility of
there being multiple NO2 monitors at one site. The
procedures for the 1-hour primary standard are entirely new.
The EPA is also making NO2-specific changes to the
deadlines, in 40 CFR 50.14, by which States must flag ambient air data
that they believe have been affected by exceptional events and submit
initial descriptions of those events, and the deadlines by which States
must submit detailed justifications to support the exclusion of that
data from EPA determinations of attainment or nonattainment with the
NAAQS. The deadlines now contained in 40 CFR 50.14 are generic, and are
not always appropriate for NO2 given the anticipated
schedule for the designations of areas under the final NO2
NAAQS.
The purpose of a data interpretation appendix in general is to
provide the practical details on how to make a comparison between
multi-day and possibly multi-monitor ambient air concentration data and
the level of the NAAQS, so that determinations of compliance and
violation are as objective as possible. Data interpretation guidelines
also provide criteria for determining whether there are sufficient data
to make a NAAQS level comparison at all. The regulatory language for
the pre-existing annual NO2 NAAQS, originally adopted in
1977, contained data interpretation instructions only for the issue of
data completeness. This situation contrasts with the situations for
ozone, PM2.5, PM10, and most recently Pb for
which there are detailed data interpretation appendices in 40 CFR part
50 addressing more issues that can arise in comparing monitoring data
to the NAAQS.
A. Interpretation of the Primary NAAQS for Oxides of Nitrogen for the
Annual Primary Standard
The purpose of a data interpretation rule for the NO2
NAAQS is to give effect to the form, level, averaging time, and
indicator specified in the regulatory text at 40 CFR 50.11,
anticipating and resolving in advance various future situations that
could occur. Appendix S provides common definitions and requirements
that apply to both the annual and the 1-hour primary standards for
NO2. The common requirements concern how ambient data are to
be reported, what ambient data are to be considered (including the
issue of which of multiple monitors' data sets will be used when more
than one monitor has operated at a site), and the applicability of the
Exceptional Events Rule to the primary NO2 NAAQS.
The proposed Appendix S also addressed several issues in ways which
are specific to the individual primary NO2 standards, as
described below.
1. Proposed Interpretation of the Annual Standard
The proposed data interpretation provisions for the annual standard
are consistent with the pre-existing instructions included along with
the statement of the level and form of the standard in 40 CFR 50.11.
These are the following: (1) At least 75% of the hours in the year must
have reported concentration data. (2) The available hourly data are
arithmetically averaged, and then rounded (not truncated) to whole
parts per billion. (3) The design value is this rounded annual average
concentration. (4) The design value is compared with the level of the
annual primary standard (expressed in parts per billion).
In the proposal, EPA noted that it would be possible to introduce
additional steps for the annual primary standard which in principle
could make the design value a more reliable indicator of actual annual
average concentration in cases where some monitoring data have been
lost. For example, averaging within a calendar quarter first and then
averaging across quarters could help compensate for uneven data capture
across the year. For some aspects of the data interpretation procedures
for some other pollutants, the current data interpretation appendices
do contain such additional steps. The proposed provisions for the
proposed 1-hour NO2 standard also incorporated some such
features.
2. Comments on Interpretation of the Annual Standard
We received four comments, all from State agencies, on data
interpretation for the annual NO2 standard. Of the four
commenters, two recommended the use of a weighted annual mean to
appropriately implement the annual primary standard. Two other
commenters asserted that there is no strong seasonality in
NO2 concentrations, and that therefore there is no need to
use a weighted annual mean or to require data completeness quarter-by-
quarter.
[[Page 6518]]
3. Conclusions on Interpretation of the Annual Standard
Upon investigating the issue of NO2 seasonality using
data from AQS as part of considering the comments, we have found that
there are notable variations in quarterly mean NO2
concentrations. It is therefore quite possible that an unweighted
annual mean calculated without a quarter-by-quarter data completeness
requirement might not represent the true annual mean as well as a
weighted annual mean calculated with a quarter-by-quarter completeness
requirement. However, the current practice of requiring 75%
completeness of all of the hours in the year and calculating the annual
mean without weighting has been retained in the final rule, because of
its simplicity and because we believe it will not interfere with
effective implementation of the annual NAAQS. No area presently is
nonattainment for or comes close to violating the annual standard.
Therefore, the choice between the two approaches can only have a
practical effect, if any, on whether at some time in the future an area
is determined to be newly violating the annual standard. If a monitor
has a complete and valid design value below the standard using the
unweighted mean approach (with only an annual data completeness
requirement) but the design value would be considered incomplete and
invalid under a hypothetical weighted mean approach (with a quarterly
completeness requirement), the monitor would in either case be
considered not to be violating and its data would not be the basis for
a nonattainment designation. If a monitor has a design value above the
standard using the unweighted annual mean approach but is incomplete
with respect to a hypothetical quarterly completeness requirement, then
the two approaches would have different implications for the
determination of a violation. A quarterly completeness requirement
would make a finding of violation impossible, unless the Administrator
chose to treat the data as if complete under another provision of the
final rule. The unweighted annual mean approach would allow but not
force a finding of violation, because the Administrator will have
discretion to make any such findings because there will be no mandatory
round of designations for the annual standard given that the annual
standard has not been revised in this review. The Administrator will be
able to consider the representativeness of the unweighted annual mean
when deciding whether to make a discretionary nonattainment
redesignation. Given that the annual standard requires only one year of
monitoring data for the calculation of a design value, little time will
be lost if the Administrator chooses to work with a State to obtain a
new design value based on more complete and/or seasonally balanced
monitoring data.
B. Interpretation of the Primary NAAQS for Oxides of Nitrogen 1-Hour
Primary Standard
1. Proposed Interpretation of the 1-Hour Standard
With regard to data completeness for the 1-hour primary standard
with a 4th highest daily value form, the proposed Appendix followed
past EPA practice for other NAAQS pollutants by requiring that in
general at least 75% of the monitoring data that should have resulted
from following the planned monitoring schedule in a period must be
available for the key air quality statistic from that period to be
considered valid. For the 1-hour primary NO2 NAAQS, the key
air quality statistics are the daily maximum 1-hour concentrations in
three successive years. It is important that sampling within a day
encompass the period when concentrations are likely to be highest and
that all seasons of the year are well represented. Hence, the 75%
requirement was proposed to be applied at the daily and quarterly
levels.
Recognizing that there may be years with incomplete data, the
proposed text provided that a design value derived from incomplete data
would nevertheless be considered valid in either of two situations.
First, if the design value calculated from at least four days of
monitoring observations in each of these years exceeds the level of the
1-hour primary standard, it would be valid. This situation could arise
if monitoring was intermittent but high NO2 levels were
measured on enough hours and days for the mean of the three annual 4th
high values to exceed the standard. In this situation, more complete
monitoring could not possibly have indicated that the standard was
actually met.
Second, we proposed a diagnostic data substitution test which was
intended to identify those cases with incomplete data in which it
nevertheless is very likely, if not virtually certain, that the daily
1-hour design value would have been observed to be below the level of
the NAAQS if monitoring data had been minimally complete.
It should be noted that one possible outcome of applying the
proposed substitution test is that a year with incomplete data may
nevertheless be determined to not have a valid design value and thus to
be unusable in making 1-hour primary NAAQS compliance determinations
for that 3-year period.
Also, we proposed that the Administrator have general discretion to
use incomplete data based on case-specific factors, either at the
request of a State or at her own initiative. Similar provisions exist
already for some other NAAQS.
The second version of the proposed Appendix S contained proposed
interpretation procedures for a 1-hour primary standard based on the
99th percentile daily value form. The 4th high daily value form and the
99th percentile daily value form would yield the same design value in a
situation in which every hour and day of the year has reported
monitoring data, since the 99th percentile of 365 daily values is the
4th highest value. However, the two forms diverge if data completeness
is 82% or less, because in that case the 99th percentile value is the
3rd highest (or higher) value, to compensate for the lack of monitoring
data on days when concentrations could also have been high.
Logically, provisions to address possible data incompleteness under
the 99th percentile daily value form should be somewhat different from
those for the 4th highest form. With a 4th highest form, incompleteness
should not invalidate a design value that exceeds the standard, for
reasons explained above. With the 99th percentile form, however, a
design value exceeding the standard stemming from incomplete data
should not automatically be considered valid, because concentrations on
the unmonitored days could have been relatively low, such that the
actual 99th percentile value for the year could have been lower, and
the design value could have been below the standard. The second
proposed version of Appendix S accordingly had somewhat different
provisions for dealing with data incompleteness. One difference was the
addition of another diagnostic test based on data substitution, which
in some cases can validate a design value based on incomplete data that
exceeds the standard.
The second version of the proposed Appendix S provided a table for
determining which day's maximum 1-hour concentration will be used as
the 99th percentile concentration for the year. The proposed table is
similar to one used now for the 24-hour PM2.5 NAAQS, which
is based on a 98th percentile form, but adjusted to reflect
[[Page 6519]]
a 99th percentile form for the 1-hour primary NO2 standard.
The proposed Appendix S also provided instructions for rounding (not
truncating) the average of three annual 99th percentile hourly
concentrations before comparison to the level of the primary NAAQS.
2. Comments on Interpretation of the 1-Hour Standard
Three commenters expressed the view that the 75% completion per
quarter requirement should apply with respect to the 1-hour standard. A
fourth commenter recommended that the requirement be increased to 82%.
Another person commented that the requirement of 75% of the hours in a
day is too stringent. The commenter noted that it would be
inappropriate not to count the day if the maximum concentration
observed in the hours measured is sufficiently high to make a
difference with regard to compliance with the NAAQS. A comment was
received that the substitution test should not be included, on the
grounds that nonattainment should not be declared without irrefutable
proof. This commenter also said that the same completeness requirement
as used for nonattainment should be used for attainment. We received
one comment that the computation of design values where multiple
monitors are present at a site should be averaged and not taken from a
designated primary monitor.
3. Conclusions on Interpretation of the 1-Hour Standard
Consistent with the Administrator's decision to adopt a 98th
percentile form for the 1-hour NAAQS, the final version of Appendix S
is based on that form. Table 1 has been revised from the version that
was proposed, so that it results in the selection of the 98th
percentile value rather than the 99th percentile value.
We agree with the three comments expressing the view that the
requirement for 75% data completeness per quarter should apply with
respect to the 1-hour standard. A fourth comment recommended that the
requirement be increased to 82%. We believe 82% is too stringent
because of the number of monitors that would not achieve such a
requirement and we believe that 75% captures the season. We agree that
an incomplete day should be counted if the maximum concentration
observed in the hours measured is sufficiently high to make a
difference with regard to compliance with the NAAQS, and we have
accounted for that in section 3.2.c.i by validating the design value if
it is above the level of the primary 1-hour standard when at least 75
percent of the days in each quarter have at least one reported hourly
value. We agree that substitution should not be used for the
establishment of attainment/nonattainment. The commenter who remarked
on this issue appears not to have understood that the specific proposed
substitution tests have essentially zero probability of making a clean
area fail the NAAQS, or vice versa, because the substituted values are
chosen to be conservative against such an outcome. As noted in section
3.2(c)(i), when substitution is used, the 3-year design value based on
the data actually reported, not the ``test design value'', shall be
used as the valid design value.
In the course of considering the above comment regarding data
substitution tests to be used in cases of data incompleteness, EPA has
realized that there could be some cases of data incompleteness in which
the proposed procedure for calculating the 1-hour design value might
result in an in appropriately low design value. As proposed, only days
with measurements for at least 75% of the hours in the day would be
considered in any way when identifying the 99th percentile value (99th
for purposes of the adopted NAAQS). However, there could be individual
hours in other, incompletely monitored days that had measured
concentrations higher than the identified 98th percentile value from
the complete days. It would be inappropriate not to consider those
hours and days in some way. However, if all days with at least one
hourly concentration were used to identify the 99th percentile value
without any regard to their incompleteness, this could also result in a
design value that is biased low because the extra days could increase
the number of ``annual number of days with valid data'' enough to
affect which row of Table 1 of Appendix S is used. It could, for
example, result in the 8th highest ranked daily maximum concentration
being identified as the 98th percentile value (based on Table 1 of
Appendix S) rather than a higher ranked concentration; this would also
be inappropriate because days which were not monitored intensively
enough to give a reasonable likelihood of catching the maximum hourly
concentration would in effect be treated as if they had such a
likelihood. For example, 50 days with only one hourly measurement
during a time of day with lower concentrations would ``earn'' the State
the right to drop one notch lower in the ranking of days when
identifying the 98th percentile day, inappropriately. The final version
of Appendix S solves this problem by providing that two procedures be
used to identifying the 98th percentile value, the first based only on
days with 75% data completeness and the second based on all days with
at least one hourly measurement. The final design value is the higher
of the two values that result from these two procedures.
With regard to situations with multiple monitors operating at one
site, we think as discussed in the proposal, that designation of a
primary monitor is preferable to averaging the data from multiple
monitors based on administrative simplicity and transparency for the
public, and is unbiased with respect to compliance outcome provided the
State is able to make the designation only before any data has been
collected.
Finally, as proposed, the final version of Appendix S has a cross
reference to the Exceptional Events Rule (40 CFR 50.14) with regard to
the exclusion of data affected by exceptional events. In addition, the
specific steps for including such data in completeness calculations
while excluding such data from actual design value calculations is
clarified in Appendix S.
C. Exceptional Events Information Submission Schedule
The Exceptional Events Rule at 40 CFR 50.14 contains generic
deadlines for a State to submit to EPA specified information about
exceptional events and associated air pollutant concentration data. A
State must initially notify EPA that data has been affected by an event
by July 1 of the year after the data are collected; this is done by
flagging the data in AQS and providing an initial event description.
The State must also, after notice and opportunity for public comment,
submit a demonstration to justify any claim within 3 years after the
quarter in which the data were collected. However, if a regulatory
decision based on the data (for example, a designation action) is
anticipated, the schedule to flag data in AQS and submit complete
documentation to EPA for review is foreshortened, and all information
must be submitted to EPA no later than one year before the decision is
to be made.
These generic deadlines are suitable for the period after initial
designations have been made under a NAAQS, when the decision that may
depend on data exclusion is a redesignation from attainment to
nonattainment or from nonattainment to attainment. However, these
deadlines present problems with respect to initial designations under a
newly revised NAAQS. One problem is
[[Page 6520]]
that some of the deadlines, especially the deadlines for flagging some
relevant data, may have already passed by the time the revised NAAQS is
promulgated. Until the level and form of the NAAQS have been
promulgated a State does not know whether the criteria for excluding
data (which are tied to the level and form of the NAAQS) were met on a
given day. The only way a State could guard against this possibility is
to flag all data that could possibly be eligible for exclusion under a
future NAAQS. This could result in flagging far more data than will
eventually be eligible for exclusion. EPA believes this is an
inefficient use of State and EPA resources, and is potentially
confusing and misleading to the public and regulated entities. Another
problem is that it may not be feasible for information on some
exceptional events that may affect final designations to be collected
and submitted to EPA at least one year in advance of the final
designation decision. This could have the unintended consequence of EPA
designating an area nonattainment as a result of uncontrollable natural
or other qualified exceptional events.
When Section 50.14 was revised in March 2007, EPA was mindful that
designations were needed under the recently revised PM2.5
NAAQS, so exceptions to the generic deadline were included for
PM2.5. The EPA was also mindful that similar issues would
arise for subsequent new or revised NAAQS. The Exceptional Events Rule
at section 50.14(c)(2)(v) indicates ``when EPA sets a NAAQS for a new
pollutant, or revises the NAAQS for an existing pollutant, it may
revise or set a new schedule for flagging data for initial designation
of areas for those NAAQS.''
EPA proposed revised exceptional event data flagging and
documentation deadlines in FR 34404 [Federal Register/Vol. 74, No. 134/
Wednesday, July 15, 2009/Proposed Rules] and invited comments from the
public. The Agency received no comments related to the revised proposed
schedule for NO2 exceptional event data flagging and
documentation deadlines.
For the specific case of NO2, EPA anticipates that
initial designations under the revised NAAQS may be made by January 22,
2012 based on air quality data from the years 2008-2010. (See Section
VI below for more detailed discussion of the designation schedule and
what data EPA intends to use.) If final designations are made by
January 22, 2012, all events to be considered during the designations
process must be flagged and fully documented by States one year prior
to designations, by January 22, 2011. This date also coincides with the
Clean Air Act deadline for Governors to submit to EPA their
recommendations for designating all areas of their States.
The final rule text at the end of this notice shows the changes
that will apply if a revised NO2 NAAQS is promulgated by
January 22, 2010, and designations are made two years after
promulgation of a NO2 NAAQS revision.
Table 1 below summarizes the data flagging and documentation
deadlines corresponding to the two year designation schedule discussed
in this section. If the promulgation date for a revised NO2
NAAQS occurs on a different date than January 22, 2010, EPA will revise
the final NO2 exceptional event flagging and documentation
submission deadlines accordingly to provide States with reasonably
adequate opportunity to review, identify, and document exceptional
events that may affect an area designation under a revised NAAQS.
Table 1--Schedule for Exceptional Event Flagging and Documentation Submission for Data To Be Used in
Designations Decisions for New or Revised NAAQS
----------------------------------------------------------------------------------------------------------------
Air quality
NAAQS pollutant/standard/(level)/ data collected Event flagging & initial Detailed documentation
promulgation date for calendar description deadline submission deadline
year
----------------------------------------------------------------------------------------------------------------
NO2/1-Hour Standard (100 PPB)........ 2008 July 1, 2010 \a\........ January 22, 2011.
2009 July 1, 2010............ January 22, 2011.
2010 April 1, 2011\a\........ July 1, 2011.\a\
----------------------------------------------------------------------------------------------------------------
\a\ Indicates change from general schedule in 40 CFR 50.14.
Note: EPA notes that the table of revised deadlines only applies to data EPA will use to establish the final
initial designations for new or revised NAAQS. The general schedule applies for all other purposes, most
notably, for data used by EPA for redesignations to attainment.
V. Designation of Areas
A. Proposed Process
The CAA requires EPA and the States to take steps to ensure that
the new or revised NAAQS are met following promulgation. The first step
is to identify areas of the country that do not meet the new or revised
NAAQS. Section 107(d)(1) provides that, ``By such date as the
Administrator may reasonably require, but not later than 1 year after
promulgation of a new or revised NAAQS for any pollutant under section
109, the Governor of each State shall * * * submit to the Administrator
a list of all areas (or portions thereof) in the State'' that should be
designated as nonattainment, attainment, or unclassifiable for the new
NAAQS. Section 107(d)(1)(B)(i) further provides, ``Upon promulgation or
revision of a NAAQS, the Administrator shall promulgate the
designations of all areas (or portions thereof) * * * as expeditiously
as practicable, but in no case later than 2 years from the date of
promulgation.''
No later than 120 days prior to promulgating designations, EPA is
required to notify States of any intended modifications to their
designations as EPA may deem necessary. States then have an opportunity
to comment on EPA's tentative decision. Whether or not a State provides
a recommendation, the EPA must promulgate the designation that it deems
appropriate.
Accordingly, Governors must submit their initial NO2
designation recommendations to EPA no later than January 2011. If the
Administrator intends to modify any State's recommendation, the EPA
will notify the Governor no later than 120 days prior to designations
in January 2012. States that believe the Administrator's modification
is inappropriate will have an opportunity to demonstrate why they
believe their recommendation is more appropriate before designations
are finalized.
B. Public Comments
Several industry commenters requested that EPA slow the timeline
for implementing a near-roadway monitoring network and designating
roadway areas because they believe EPA lacks significant information
about the implementation and performance of a national, near-roadway
monitoring network. Two commenters also requested that if a near-
roadway monitoring network is deployed, that 1-hour NO2
standards be made more
[[Page 6521]]
lenient until the next review period so that more information will be
available about near-roadway NO2 concentrations before a
stringent standard is selected.
A response to commenters' requests that EPA slow the monitoring
implementation schedule and the request that EPA make the 1-hour
NO2 standard more lenient until the next review period are
addressed in sections III.B.5 and II.F.4.D, respectively.
Section 110(d)(1)(B) requires the EPA to designate areas no later
than 2 years following promulgation of a new or revised NAAQS (i.e., by
January 2012). While the CAA provides the Agency an additional third
year from promulgation of a NAAQS to complete designations in the event
that there is insufficient information to make NAAQS compliance
determinations, we anticipate that delaying designations for an
additional year would not result in significant new data to inform the
initial designations. A near-roadway monitoring network is not expected
to be fully deployed until January 2013 therefore, EPA must proceed
with initial designations using air quality data from the existing
NO2 monitoring network. Because none of the current
NO2 monitors are sited to measure near-roadway ambient air,
we expect that most areas in the country with current NO2
monitors will not violate the new NO2 NAAQS. In the event
that a current NO2 monitor indicates a violation of the
revised standards, EPA intends to designate such areas
``nonattainment'' no later than 2 years following promulgation of the
revised standards. We intend to designate the rest of the country as
``unclassifiable'' for the revised NO2 NAAQS until
sufficient air quality data is collected from a near-roadway monitoring
network. Once the near-roadway network is fully deployed and 3 years of
air quality data are available, the EPA has authority under the CAA to
redesignate areas as appropriate from ``unclassifiable'' to
``attainment'' or ``nonattainment.'' We anticipate that sufficient data
to conduct designations would be available after 2015.
A number of commenters, largely from industry groups, focused on
the concern that a near-roadway monitoring network would lead to
regional nonattainment on the basis of high NO2
concentrations found near roadways. These commenters requested that any
future nonattainment areas be limited to the area directly surrounding
roadways found to have above-standard NO2 concentrations.
The CAA requires that any area that does not meet a NAAQS or that
contributes to a violation in a nearby area that does not meet the
NAAQS be designated ``nonattainment.'' States and EPA will need to
determine which sources and activities contribute to a NAAQS violation
in each area. Depending on the circumstances in each area this may
include sources and activities in areas beyond the area directly
surrounding a major roadway. EPA intends to issue nonattainment area
boundary guidance after additional information is gathered on the
probable contributors to violating near-roadway NO2
monitors.
C. Final Designations Process
The EPA intends to promulgate initial NO2 designations
by January 2012 (2 years after promulgation of the revised NAAQS).
Along with today's action EPA is also promulgating new monitoring rules
that focus on roadways. As noted in section III, States must site
required NO2 near-roadway monitors and have them operational
by January 1, 2013. States will need an additional 3 years thereafter
to collect air quality data in order to determine compliance with the
revised NAAQS. This means that a full set of air quality data from the
new network will not be available until after 2015. Since we anticipate
that data from the new network will not be available prior to the CAA
designation deadlines discussed above, the EPA intends to complete
initial NO2 designations by January 2012 using the 3 most
recent years of quality-assured air quality data from the current
monitoring network, which would be for the years 2008-2010. The EPA
will designate as ``nonattainment'' any areas with NO2
monitors recording violations of the revised NO2 NAAQS. We
intend to designate all other areas of the country as
``unclassifiable'' to indicate that there is insufficient data to
determine whether or not they are attaining the revised NO2
NAAQS.
Once the NO2 monitors are positioned in locations
meeting the near-roadway siting requirements and monitoring data become
available, the Agency has authority under section 107(d)(3) of the CAA
to redesignate areas as appropriate from ``unclassifiable'' to
``attainment'' or ``nonattainment.'' The EPA intends to issue guidance
on the factors that States should consider when determining
nonattainment boundaries after additional information is gathered on
the probable contributors to violating near-roadway NO2
monitors.
VI. Clean Air Act Implementation Requirements
This section of the preamble discusses the Clean Air Act (CAA)
requirements that States and emissions sources must address when
implementing new or revised NO2 NAAQS based on the structure
outlined in the CAA and existing rules.\26\ EPA may provide additional
guidance in the future, as necessary, to assist States and emissions
sources to comply with the CAA requirements for implementing new or
revised NO2 NAAQS.
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\26\ Since EPA is retaining the annual standard without
revision, the discussion in this section relates to implementation
of the proposed 1-hour standard, rather than the annual standard.
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The CAA assigns important roles to EPA, States, and, in specified
circumstances, Tribal governments to achieve the NAAQS. States have the
primary responsibility for developing and implementing State
Implementation Plans (SIPs) that contain State measures necessary to
achieve the air quality standards in each area. EPA provides assistance
to States by providing technical tools, assistance, and guidance,
including information on the potential control measures that may help
areas meet the standards.
States are primarily responsible for ensuring attainment and
maintenance of ambient air quality standards once they have been
established by EPA. Under section 110 of the CAA, 42 U.S.C. 7410, and
related provisions, States are required to submit, for EPA approval,
SIPs that provide for the attainment and maintenance of such standards
through control programs directed at sources of NO2
emissions. If a State fails to adopt and implement the required SIPs by
the time periods provided in the CAA, the EPA has responsibility under
the CAA to adopt a Federal Implementation Plan (FIP) to assure that
areas attain the NAAQS in an expeditious manner.
The States, in conjunction with EPA, also administer the prevention
of significant deterioration (PSD) program for NO2 and
nonattainment new source review (NSR). See sections 160-169 of the CAA.
In addition, Federal programs provide for nationwide reductions in
emissions of NO2 and other air pollutants under Title II of
the Act, 42 U.S.C. 7521-7574, which involves controls for automobiles,
trucks, buses, motorcycles, nonroad engines, and aircraft emissions;
the new source performance standards (NSPS) for stationary sources
under section 111 of the CAA, 42 U.S.C. 7411.
CAA Section 301(d) authorizes EPA to treat eligible Indian Tribes
in the same manner as States (TAS) under the CAA and requires EPA to
promulgate regulations specifying the provisions of the statute for
which such treatment is appropriate. EPA has promulgated these
[[Page 6522]]
regulations--known as the Tribal Authority Rule or TAR--at 40 CFR Part
49. See 63 FR 7254 (February 12, 1998). The TAR establishes the process
for Indian Tribes to seek TAS eligibility and sets forth the CAA
functions for which TAS will be available. Under the TAR, eligible
Tribes may seek approval for all CAA and regulatory purposes other than
a small number of functions enumerated at section 49.4. Implementation
plans under section 110 are included within the scope of CAA functions
for which eligible Tribes may obtain approval. Section 110(o) also
specifically describes Tribal roles in submitting implementation plans.
Eligible Indian Tribes may thus submit implementation plans covering
their reservations and other areas under their jurisdiction.
Under the CAA and TAR, Tribes are not, however, required to apply
for TAS or implement any CAA program. In promulgating the TAR EPA
explicitly determined that it was not appropriate to treat Tribes
similarly to States for purposes of, among other things, specific plan
submittal and implementation deadlines for NAAQS-related requirements.
40 CFR 49.4(a). In addition, where Tribes do seek approval of CAA
programs, including section 110 implementation plans, the TAR provides
flexibility and allows them to submit partial program elements, so long
as such elements are reasonably severable--i.e., ``not integrally
related to program elements that are not included in the plan
submittal, and are consistent with applicable statutory and regulatory
requirements.'' 40 CFR 49.7.
To date, very few Tribes have sought TAS for purposes of section
110 implementation plans. However, some Tribes may be interested in
pursuing such plans to implement today's proposed standard. As noted
above, such Tribes may seek approval of partial, reasonably severable
plan elements, or they may seek to implement all relevant components of
an air quality program for purposes of meeting the requirements of the
Act. In several sections of this preamble, EPA describes the various
roles and requirements States will address in implementing today's
proposed standard. Such references to States are generally intended to
include eligible Indian Tribes to the extent consistent with the
flexibility provided to Tribes under the TAR. Where Tribes do not seek
TAS for section 110 implementation plans, EPA will promulgate Federal
implementation plans as ``necessary or appropriate to protect air
quality.'' 40 CFR 49.11(a). EPA also notes that some Tribes operate air
quality monitoring networks in their areas. For such monitors to be
used to measure attainment with this primary NAAQS for NO2,
the criteria and procedures identified in this rule would apply.
A. Classifications
1. Proposal
Section 172(a)(1)(A) of the CAA authorizes EPA to classify areas
designated as nonattainment for the purpose of applying an attainment
date pursuant to section 172(a)(2), or for other reasons. In
determining the appropriate classification, EPA may consider such
factors as the severity of the nonattainment problem and the
availability and feasibility of pollution control measures (see section
172(a)(1)(A) of the CAA). The EPA may classify NO2
nonattainment areas, but is not required to do so. The primary reason
to establish classifications is to set different deadlines for each
class of nonattainment area to complete the planning process and to
provide for different attainment dates based upon the severity of the
nonattainment problem for the affected area. However, the CAA
separately establishes specific planning and attainment deadlines for
certain pollutants including NO2 in sections 191 and 192: 18
months from nonattainment designation for the submittal of an
attainment plan, and as expeditiously as possible, but no later than 5
years from nonattainment designation for areas to attain the standard.
In the proposal, EPA stated its belief that classifications are
unnecessary in light of these relatively short deadlines.
2. Public Comments
One commenter stated that they disagree with EPA's decision not to
impose non-attainment classifications on areas with measured near-road
NO2 concentrations in excess of the new NO2
standard, and urged EPA to provide a graduated non-attainment
classification system for the new standard. According to the commenter,
``a classification system defining higher levels of non-attainment with
increasingly stringent requirements at those levels is one that allows
for finer calibration of air quality regulatory response defined at the
Federal level.''
As stated in the proposed rule, Section 192(a), of part D, of the
CAA specifically provides an attainment date for areas designated as
nonattainment for the NO2 NAAQS. Therefore, EPA has legal
authority to classify NO2 nonattainment areas, but the 5-
year attainment date addressed under section 192(a) cannot be extended
pursuant to section 172(a)(2)(D). Based on this limitation, EPA
proposed not to establish classifications within the 5- year interval
for attaining any new or revised NO2 NAAQS. It is also EPA's
belief that given the short deadlines that States have to develop and
submit SIP's and for areas to achieve emissions reductions in order to
attain the standard within the 5 year attainment period, a graduated
classifications system would not be appropriate. Therefore, EPA is
using it's discretion under the CAA not to establish classifications.
3. Final
EPA is not making any changes to the discussion on classifications
in the proposed rule. Therefore, there will be no classifications for
the revised NO2 NAAQS.
B. Attainment Dates
The maximum deadline by which an area is required to attain the
NO2 NAAQS is determined from the effective date of the
nonattainment designation for the affected area. For areas designated
nonattainment for the revised NO2 NAAQS, SIPs must provide
for attainment of the NAAQS as expeditiously as practicable, but no
later than 5 years from the date of the nonattainment designation for
the area (see section 192(a) of the CAA). The EPA will determine
whether an area has demonstrated attainment of the NO2 NAAQS
by evaluating air quality monitoring data consistent with the form of
the NAAQS for NO2 if revised, which will be codified at 40
CFR part 50, Appendix F.
1. Attaining the NAAQS
a. Proposal
In order for an area to be redesignated as attainment, the State
must comply with the five requirements as provided under section
107(d)(3)(E) of the CAA. This section requires that:
--EPA must have determined that the area has met the NO2
NAAQS;
--EPA has fully approved the State's implementation plan;
--The improvement in air quality in the affected area is due to
permanent and enforceable reductions in emissions;
--EPA has fully approved a maintenance plan for the area; and
--The State(s) containing the area have met all applicable requirements
under section 110 and part D.
b. Final
EPA did not receive any comments on this aspect of the proposed
rule and is not making any changes to the
[[Page 6523]]
discussion on attaining the NAAQS in the proposed rule.
2. Consequences of Failing To Attain by the Statutory Attainment Date
a. Proposal
Any NO2 nonattainment area that fails to attain by its
statutory attainment date would be subject to the requirements of
sections 179(c) and (d) of the CAA. EPA is required to make a finding
of failure to attain no later than 6 months after the specified
attainment date and publish a notice in the Federal Register. The State
would be required to submit an implementation plan revision, no later
than one year following the effective date of the Federal Register
notice making the determination of the area's failure to attain, which
demonstrates that the standard will be attained as expeditiously as
practicable, but no later than 5 years from the effective date of EPA's
finding that the area failed to attain. In addition, section 179(d)(2)
provides that the SIP revision must include any specific additional
measures as may be reasonably prescribed by EPA, including ``all
measures that can be feasibly implemented in the area in light of
technological achievability, costs, and any nonair quality and other
air quality-related health and environmental impacts.''
b. Final
EPA did not receive any comments on this aspect of the proposed
rule and is not making any changes to the discussion on consequences of
failing to attain by the statutory attainment date in the proposed
rule.
C. Section 110(a)(2) NAAQS Infrastructure Requirements
1. Proposal
Section 110(a)(2) of the CAA requires all States to develop and
maintain a solid air quality management infrastructure, including
enforceable emission limitations, an ambient monitoring program, an
enforcement program, air quality modeling, and adequate personnel,
resources, and legal authority. Section 110(a)(2)(D) also requires
State plans to prohibit emissions from within the State which
contribute significantly to nonattainment or maintenance areas in any
other State, or which interfere with programs under part C to prevent
significant deterioration of air quality or to achieve reasonable
progress toward the national visibility goal for Federal class I areas
(national parks and wilderness areas).
Under section 110(a)(1) and (2) of the CAA, all States are required
to submit SIPs to EPA which demonstrate that basic program elements
have been addressed within 3 years of the promulgation of any new or
revised NAAQS. Subsections (A) through (M) of section 110(a)(2) listed
below, set forth the elements that a State's program must contain in
the SIP.\27\ The list of section 110(a)(2) NAAQS implementation
requirements are the following:
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\27\ Two elements identified in section 110(a)(2) are not listed
below because, as EPA interprets the CAA, SIPs incorporating any
necessary local nonattainment area controls would not be due within
3 years, but rather are due at the time the nonattainment area
planning requirements are due. These elements are: (1) Emission
limits and other control measures, section 110(a)(2)(A), and (2)
Provisions for meeting part D, section 110(a)(2)(I), which requires
areas designated as nonattainment to meet the applicable
nonattainment planning requirements of part D, title I of the CAA.
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Ambient air quality monitoring/data system: Section
110(a)(2)(B) requires SIPs to provide for setting up and operating
ambient air quality monitors, collecting and analyzing data and making
these data available to EPA upon request.
Program for enforcement of control measures: Section
110(a)(2)(C) requires SIPs to include a program providing for
enforcement of measures and regulation and permitting of new/modified
sources.
Interstate transport: Section 110(a)(2)(D) requires SIPs
to include provisions prohibiting any source or other type of emissions
activity in the State from contributing significantly to nonattainment
in another State or from interfering with measures required to prevent
significant deterioration of air quality or to protect visibility.
Adequate resources: Section 110(a)(2)(E) requires States
to provide assurances of adequate funding, personnel and legal
authority for implementation of their SIPs.
Stationary source monitoring system: Section 110(a)(2)(F)
requires States to establish a system to monitor emissions from
stationary sources and to submit periodic emissions reports to EPA.
Emergency power: Section 110(a)(2)(G) requires States to
include contingency plans, and adequate authority to implement them,
for emergency episodes in their SIPs.
Provisions for SIP revision due to NAAQS changes or
findings of inadequacies: Section 110(a)(2)(H) requires States to
provide for revisions of their SIPs in response to changes in the
NAAQS, availability of improved methods for attaining the NAAQS, or in
response to an EPA finding that the SIP is inadequate.
Consultation with local and Federal government officials:
Section 110(a)(2)(J) requires States to meet applicable local and
Federal government consultation requirements when developing SIP and
reviewing preconstruction permits.
Public notification of NAAQS exceedances: Section
110(a)(2)(J) requires States to adopt measures to notify the public of
instances or areas in which a NAAQS is exceeded.
PSD and visibility protection: Section 110(a)(2)(J) also
requires States to adopt emissions limitations, and such other
measures, as may be necessary to prevent significant deterioration of
air quality in attainment areas and protect visibility in Federal Class
I areas in accordance with the requirements of CAA Title I, part C.
Air quality modeling/data: Section 110(a)(2)(K) requires
that SIPs provide for performing air quality modeling for predicting
effects on air quality of emissions of any NAAQS pollutant and
submission of data to EPA upon request.
Permitting fees: Section 110(a)(2)(L) requires the SIP to
include requirements for each major stationary source to pay permitting
fees to cover the cost of reviewing, approving, implementing and
enforcing a permit.
Consultation and participation by affected local
government: Section 110(a)(2)(M) requires States to provide for
consultation and participation by local political subdivisions affected
by the SIP.
2. Final
EPA did not receive any comments on this aspect of the proposed
rule and is not making any changes to the discussion on section
110(a)(2) NAAQS infrastructure requirements in the proposed rule.
D. Attainment Planning Requirements
1. Nonattainment Area SIPs
a. Proposal
Any State containing an area designated as nonattainment with
respect to the NO2 NAAQS must develop for submission a SIP
meeting the requirements of part D, Title I, of the CAA, providing for
attainment by the applicable statutory attainment date (see sections
191(a) and 192(a) of the CAA). As indicated in section 191(a) all
components of the NO2 part D SIP must be submitted within 18
months of the effective date of an area's designation as nonattainment.
Section 172 of the CAA includes general requirements for all
designated nonattainment areas. Section 172(c)(1)
[[Page 6524]]
requires that each nonattainment area plan ``provide for the
implementation of all reasonably available control measures (RACM) as
expeditiously as practicable (including such reductions in emissions
from existing sources in the area as may be obtained through the
adoption, at a minimum, of Reasonably Available Control Technology
(RACT)), and shall provide for attainment of the national primary
ambient air quality standards.'' States are required to implement RACM
and RACT in order to attain ``as expeditiously as practicable''.
Section 172(c) requires States with nonattainment areas to submit a
SIP for these areas which contains an attainment demonstration that
shows that the affected area will attain the standard by the applicable
statutory attainment date. The State must also show that the area will
attain the standards as expeditiously as practicable, and it must
include an analysis of whether implementation of reasonably available
measures will advance the attainment date for the area.
Part D SIPs must also provide for reasonable further progress (RFP)
(see section 172(c)(2) of the CAA). The CAA defines RFP as ``such
annual incremental reductions in emissions of the relevant air
pollution as are required by part D, or may reasonably be required by
the Administrator for the purpose of ensuring attainment of the
applicable NAAQS by the applicable attainment date.'' (See section 171
of the CAA.) Historically, for some pollutants, RFP has been met by
showing annual incremental emission reductions sufficient to maintain
generally linear progress toward attainment by the applicable
attainment date.
All NO2 nonattainment area SIPs must include contingency
measures which must be implemented in the event that an area fails to
meet RFP or fails to attain the standards by its attainment date. (See
section 172(c)(9).) These contingency measures must be fully adopted
rules or control measures that take effect without further action by
the State or the Administrator. The EPA interprets this requirement to
mean that the contingency measures must be implemented with only
minimal further action by the State or the affected sources with no
additional rulemaking actions such as public hearings or legislative
review.
Emission inventories are also critical for the efforts of State,
local, and Federal agencies to attain and maintain the NAAQS that EPA
has established for criteria pollutants including NO2.
Section 191(a) in conjunction with section 172(c) requires that areas
designated as nonattainment for NO2 submit an emission
inventory to EPA no later than 18 months after designation as
nonattainment. In the case of NO2, sections 191(a) and
172(c) also require that States submit periodic emission inventories
for nonattainment areas. The periodic inventory must include emissions
of NO2 for point, nonpoint, mobile (on-road and non-road),
and area sources.
b. Public Comments
Several commenters indicated that EPA should take steps to ensure
that States actually require mobile source emissions reductions in
order to attain the NO2 NAAQS as opposed to controlling
point sources. Another commenter went further and stated that States be
required to control on-road emissions as opposed to emissions from
stationary sources and in particular EGUs. This commenter also
indicated that EPA should delay nonattainment designations until States
had a cost effective means of reducing on-road emissions of
NO2.
EPA cannot require States to develop a SIP that only addresses one
type of source, in this case on-road mobile sources. States may select
appropriate control measures to attain the NAAQS and EPA must approve
them if they otherwise meet all applicable requirements of the Act. See
CAA 116. EPA expects that States will evaluate a range of control
measures that will reduce NO2 emissions within the time
allowed to attain the standard. This would include the emissions
reductions attributable to Federal controls on on-road and non-road
mobile sources, and controls that they have put in place to reduce
NOX emissions in order to attain the 8-hour ozone NAAQS and/
or the PM2.5 NAAQS. If these existing controls are not
sufficient for an area to reach attainment with the NO2
NAAQS, EPA would expect the State to implement additional control
measures that would bring the area into attainment by the deadline. For
a designation based on data from a near roadway monitor EPA would
expect the States to give primary consideration to controlling
emissions from on-road sources; however, it is likely that other types
of sources contribute to the concentrations that are measured at a near
roadway monitor and a State may decide to implement controls on these
other contributing sources.
The Clean Air Act requires that EPA finalize designations within
two years after a NAAQS is revised unless the available air quality
data is insufficient to make designations by that time. In that case,
EPA must finalize designations within three years after the NAAQS is
revised. As discussed elsewhere in today's final rule, EPA believes
that it has sufficient data to make designations within two years and
that most areas will be designated as unclassifiable at that time.
Taking the additional year provided by the CAA would not allow
additional data from the new near roadway monitors to be factored into
the designations process in any event. Therefore, it is EPA's intention
to designate areas within two years as required by the Act. EPA intends
to redesignate areas once it has sufficient data from the new
monitoring network to designate areas as clearly attaining or not
attaining the standard.
c. Final
The EPA is not making any changes to the discussion on
nonattainment area SIPs in the proposed rule.
2. New Source Review and Prevention of Significant Deterioration
Requirements
a. Proposal
The Prevention of Significant Deterioration (PSD) and nonattainment
New Source Review (NSR) programs contained in parts C and D of Title I
of the CAA govern preconstruction review of any new or modified major
stationary sources of air pollutants regulated under the CAA as well as
any precursors to the formation of that pollutant when identified for
regulation by the Administrator.\28\ The EPA rules addressing these
programs can be found at 40 CFR 51.165, 51.166, 52.21, 52.24, and part
51, appendix S. States which have areas designated as nonattainment for
the NO2 NAAQS must submit, as a part of the SIP due 18
months after an area is designated as nonattainment, provisions
requiring permits for the construction and operation of new or modified
stationary sources anywhere in the nonattainment area. SIPs that
address the PSD requirements related to attainment areas are due no
later than 3 years after the promulgation of a revised NAAQS for
NO2.
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\28\ The terms ``major'' and ``minor'' define the size of a
stationary source, for applicability purposes, in terms of an annual
emissions rate (tons per year, tpy) for a pollutant. Generally, a
minor source is any source that is not ``major.'' ``Major'' is
defined by the applicable regulations--PSD or nonattainment NSR.
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The NSR program is composed of three different permit programs:
Prevention of Significant Deterioration (PSD).
Nonattainment NSR (NA NSR).
Minor NSR.
The PSD program applies when a major source, that is located in an
area that is designated as attainment or
[[Page 6525]]
unclassifiable for any criteria pollutant, is constructed, or undergoes
a major modification.\29\ The nonattainment NSR program applies on a
pollutant-specific basis when a major source constructs or modifies in
an area that is designated as nonattainment for that pollutant. The
minor source NSR program addresses both major and minor sources which
undergo construction or modification activities that do not qualify as
major, and it applies, as necessary to assure attainment, regardless of
the designation of the area in which a source is located.
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\29\ In addition, the PSD program applies to non-criteria
pollutants subject to regulation under the Act, except those
pollutants regulated under section 112 and pollutants subject to
regulation only under section 211(o).
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The PSD requirements include but are not limited to the following:
Installation of Best Available Control Technology (BACT);
Air quality monitoring and modeling analyses to ensure
that a project's emissions will not cause or contribute to a violation
of any NAAQS or maximum allowable pollutant increase (PSD increment);
Notification of Federal Land Manager of nearby Class I
areas; and
Public comment on permit.
Nonattainment NSR requirements include but are not limited to:
Installation of Lowest Achievable Emissions Rate (LAER)
control technology;
Offsetting new emissions with creditable emissions
reductions;
A certification that all major sources owned and operated
in the State by the same owner are in compliance with all applicable
requirements under the CAA;
An alternative siting analysis demonstrating that the
benefits of a proposed source significantly outweigh the environmental
and social costs imposed as a result of its location, construction, or
modification; and
Public comment on the permit.
Minor NSR programs must meet the statutory requirements in section
110(a)(2)(C) of the CAA which requires ``* * * regulation of the
modification and construction of any stationary source * * * as
necessary to assure that the [NAAQS] are achieved.'' Areas which are
newly designated as nonattainment for the NO2 NAAQS as a
result of any changes made to the NAAQS will be required to adopt a
nonattainment NSR program to address major sources of NO2
where the program does not currently exist for the NO2 NAAQS
and may need to amend their minor source program as well. Prior to
adoption of the SIP revision addressing major source nonattainment NSR
for NO2 nonattainment areas, the requirements of 40 CFR part
51, appendix S may apply.
b. Public Comments
One commenter claimed that EPA's setting of a more stringent
standard, i.e., short-term NO2 NAAQS, could have important
implications for NSR and PSD and title V permits. Another commenter
indicated that the promulgation of a new 1-hr NO2 short-term
standard could create the need for a short-term PSD increment. Another
commenter stated that a 1-hr NO2 Significant Impact Level
(SIL) should be developed.
The EPA acknowledges that a decision to promulgate a new short-term
NO2 NAAQS will clearly have implications for the air
permitting process. The full extent of how a new short-term
NO2 NAAAQS will affect the NSR process will need to be
carefully evaluated. First, major new and modified sources applying for
NSR/PSD permits will initially be required to demonstrate that their
proposed emissions increases of NOX will not cause or
contribute to a violation of either the annual or 1-hour NO2
NAAQS and the annual PSD increment. In addition, we believe that
section 166 of the CAA authorizes us to consider the need to promulgate
a new 1-hour increment. Historically, EPA has developed increments for
each applicable averaging period for which a NAAQS has been
promulgated. However, increments for a particular pollutant do not
necessarily need to match the averaging periods that have been
established for NAAQS for the same pollutant. Environmental Defense
Fund, Inc. v. EPA, 898 F.2d 183, 189-190 (DC Cir. 1990) (`` * * * the
`goals and purposes' of the PSD program, set forth in 160, are not
identical to the criteria on which the ambient standards are based.'')
Thus, we would need to evaluate the need for a new 1-hour
NO2 increment in association with the goals and purposes of
the statutory PSD program requirements.
We also believe that there may be a need to revise the screening
tools currently used under the NSR/PSD program for completing
NO2 analyses. These screening tools include the significant
impact levels (SILs), as mentioned by one commenter, but also include
the significant emissions rate for emissions of NOX and the
significant monitoring concentration (SMC) for NO2. EPA
intends to evaluate the need for possible changes or additions to each
of these important screening tools for NOX/NO2
due to the addition of a 1-hour NO2 NAAQS. If changes or
additions are deemed necessary, EPA will propose any such changes for
public notice and comment in a separate action.
c. Final
The EPA is not making any changes to the discussion concerning the
requirements for NSR and PSD as stated in the proposed rule.
3. General Conformity
a. Proposal
Section 176(c) of the CAA, as amended (42 U.S.C. 7401 et seq.),
requires that all Federal actions conform to an applicable
implementation plan developed pursuant to section 110 and part D of the
CAA. The EPA rules, developed under the authority of section 176(c) of
the CAA, prescribe the criteria and procedures for demonstrating and
assuring conformity of Federal actions to a SIP. Each Federal agency
must determine that any actions covered by the general conformity rule
conform to the applicable SIP before the action is taken. The criteria
and procedures for conformity apply only in nonattainment areas and
those areas redesignated attainment since 1990 (``maintenance areas'')
with respect to the criteria pollutants under the CAA: \30\ carbon
monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone
(O3), particulate matter (PM2.5 and
PM10), and sulfur dioxide (SO2). The general
conformity rules apply one year following the effective date of
designations for any new or revised NAAQS.
---------------------------------------------------------------------------
\30\ Criteria pollutants are those pollutants for which EPA has
established a NAAQS under section 109 of the CAA.
---------------------------------------------------------------------------
The general conformity determination examines the impacts of direct
and indirect emissions related to Federal actions. The general
conformity rule provides several options to satisfy air quality
criteria, such as modeling or offsets, and requires the Federal action
to also meet any applicable SIP requirements and emissions milestones.
The general conformity rule also requires that notices of draft and
final general conformity determinations be provided directly to air
quality regulatory agencies and to the public by publication in a local
newspaper.
b. Final
EPA did not receive any comments on this aspect of the proposed
rule and is not making any changes to the discussion concerning general
conformity stated in the proposed rule.
[[Page 6526]]
4. Transportation Conformity
a. Proposal
Transportation conformity is required under CAA section 176(c) (42
U.S.C. 7506(c)) to ensure that transportation plans, transportation
improvement programs (TIPs) and Federally supported highway and transit
projects will not cause new air quality violations, worsen existing
violations, or delay timely attainment of the relevant NAAQS or interim
reductions and milestones. Transportation conformity applies to areas
that are designated nonattainment and maintenance for transportation-
related criteria pollutants: Carbon monoxide (CO), ozone
(O3), nitrogen dioxide (NO2), and particulate
matter (PM2.5 and PM10). Transportation
conformity for a revised NO2 NAAQS does not apply until one
year after the effective date of a nonattainment designation. (See CAA
section 176(c)(6) and 40 CFR 93.102(d)).
EPA's Transportation Conformity Rule (40 CFR 51.390, and Part 93,
Subpart A establishes the criteria and procedures for determining
whether transportation activities conform to the SIP. The EPA is not
making changes to the Transportation Conformity rule in this
rulemaking. However, in the future, EPA will review the need to conduct
a rulemaking to establish any new or revised transportation conformity
tests that would apply under a revision to the NO2 NAAQS for
transportation plans, TIPs, and applicable highway and transit
projects.
b. Public Comments
Several commenters stated that transportation conformity could stop
the funding of highway and transit projects in NO2
nonattainment areas. These commenters stated that if an area fails to
demonstrate conformity, it enters a conformity lapse and only certain
types of projects can be funded during a lapse. The commenters further
stated that the NO2 NAAQS will require more areas to
determine conformity for the first time. The commenters also expressed
concern that the NO2 NAAQS proposal did not contain
sufficient information to understand to what extent revisions to the
NAAQS, and the NO2 monitoring requirements, will result in
transportation conformity requirements for individual transportation
projects such as the need for a hot-spot analysis. The commenters
further stated that hot-spot analyses could result in needless delays
for transportation improvement projects.
With regard to the comment that more areas will have to demonstrate
conformity for the first time due to the revisions to the
NO2 NAAQS, given that today's final rule is requiring that
near roadway monitoring be carried out in urban areas with populations
greater than 350K, EPA believes that most areas with such populations
that would be designated nonattainment for NO2 are already
designated nonattainment or maintenance for one or more of the other
transportation-related criteria pollutants (ozone, PM2.5,
PM10 and carbon monoxide). As such, these areas would have
experience in making transportation conformity determinations. If areas
with no conformity experience are designated nonattainment for the
NO2 NAAQS, EPA and U.S. DOT would be available to assist
areas in implementing the transportation conformity requirements.
The commenter expressed concern that transportation conformity
could stop highway and transit funding because areas could experience a
conformity lapse and in such cases only certain types of projects could
be funded. A conformity lapse occurs when an area misses a deadline for
a required conformity determination. A new nonattainment area must
demonstrate conformity within one year after the effective date of its
designation. For any areas designated nonattainment for the revised
NO2 NAAQS in early-2012, they would have to determine
conformity within one year of the effective date of that designation
which would be in early-2013. If that date was missed, a lapse would
occur and only projects exempt from conformity such as safety projects,
transportation control measures in an approved SIP for the area and
projects or project phases that were approved by U.S. DOT before the
lapse began can proceed during the lapse. EPA's experience in
implementing the 1997 ozone and PM2.5 NAAQS shows that
nearly all areas make their initial conformity determinations within
the one-year grace period. Areas can also lapse if they fail to
determine conformity by an applicable deadline such as determining
conformity within two years after motor vehicle emissions budgets are
found adequate. However, areas that miss one of these conformity
deadlines have a one-year grace period before the lapse goes into
effect. During the grace period, the area can continue to advance
projects from the transportation plan and transportation improvement
program. EPA's experience is that areas generally are able to make a
conformity determination before the end of the grace period.
The commenter expressed concern that the NO2 NAAQS
proposal did not contain sufficient detail concerning possible project-
level requirements for transportation projects and that any
requirements for hot-spot analyses could needlessly delay
transportation projects. As EPA indicated in the NPRM, EPA is
considering whether to revise the transportation conformity rule to
establish requirements that would apply to transportation plans,
transportation improvement programs and/or transportation projects in
NO2 nonattainment and maintenance areas. If EPA concludes
that the conformity rule must be revised in light of the final
NO2 NAAQS, we will conduct notice and comment rulemaking to
accomplish the revisions. At that time interested parties will have the
opportunity to comment on any transportation conformity NPRM. This is
the same course of action that EPA has taken with respect to revising
the transportation conformity rule for the ozone and PM2.5
NAAQS.
With regard to the commenter's assertion that a requirement for
hot-spot analyses for individual projects would needlessly delay
transportation projects, EPA disagrees. First, CAA section 176(c)(1)(B)
requires that transportation projects not cause new violations or make
existing violations worse, or delay timely attainment or cause an
interim milestone to be missed. EPA would only impose a hot-spot
requirement for projects in NO2 nonattainment and
maintenance areas if they are necessary to comply with CAA conformity
requirements and therefore are needed to protect public health by
reducing exposures to unhealthy levels of NO2 that could be
created by the implementation of a proposed highway or transit project.
The public would be exposed to unhealthy levels of NO2 if a
highway or transit project caused a new violation of the NO2
NAAQS, made an existing violation worse, or delayed timely attainment
or delayed achieving an interim emissions milestone. If any delay in
the project did occur, it would not be viewed as needless as it
occurred for the important purpose of protecting the exposed public's
health. Second, EPA does not agree that requiring a hot-spot analysis
would needlessly delay projects in NO2 nonattainment areas.
Such hot-spot analyses, if they are eventually required, generally
would be done as part of the NEPA process, which these projects are
already subject to; therefore, conducting an NO2 hot-spot
analysis would not be introducing a new step to a project's approval
process, but rather would add one additional analysis which must be
completed as part of an existing project approval process.
[[Page 6527]]
c. Final
EPA is not making any changes to the discussion concerning
transportation conformity as stated in the proposed rule.
VII. Communication of Public Health Information
Information on the public health implications of ambient
concentrations of criteria pollutants is currently made available
primarily through EPA's Air Quality Index (AQI) program. This section
describes the conforming changes that were proposed, major comments
received on these changes, EPA's responses to these comments and final
decisions on the AQI breakpoints. Recognizing the importance of
revising the AQI in a timely manner to be consistent with any revisions
to the NAAQS, EPA proposed conforming changes to the AQI in connection
with the final decision on the NO2 NAAQS if revisions to the
primary standard were promulgated. Conforming changes would include
setting the 100 level of the AQI at the same level as the revised
primary NO2 NAAQS and also setting the other AQI breakpoints
at the lower end of the AQI scale (i.e., AQI values of 50 and 150). EPA
did not propose to change breakpoints at the higher end of the AQI
scale (from 200 to 500), which would apply to State contingency plans
or the Significant Harm Level (40 CFR 51.16), because the information
from this review does not inform decisions about breakpoints at those
higher levels.
With regard to an AQI value of 50, the breakpoint between the good
and moderate categories, EPA proposed to set this value to be between
0.040 and 0.053 ppm NO2, 1-hour average. EPA proposed that
the figure towards the lower end of this range would be appropriate if
the standard is set towards the lower end of the proposed range for the
standard (e.g. 80 ppb), while figures towards the higher end of the
range would be more appropriate for standards set at the higher end of
the range for the standard (e.g., 100 ppb). EPA noted that historically
this value is set at the level of the annual NAAQS, if there is one, or
one-half the level of the short-term NAAQS in the absence of an annual
NAAQS, and solicited comments on this range for an AQI of 50 and the
appropriate basis for selecting an AQI of 50 within this range.
With regard to an AQI value of 150, the breakpoint between the
unhealthy for sensitive groups and unhealthy categories, the range of
0.360 to 0.370 ppm NO2, 1-hour average, represents the
midpoint between the proposed range for the short-term standard and the
level of an AQI value of 200 (0.64 ppm NO2, 1-hour average).
Therefore, EPA proposed to set the AQI value of 150 to be between 0.360
and 0.370 ppm NO2, 1-hour average.
EPA received comments from several State environmental agencies and
organizations of State and local agencies that generally expressed the
view that the AQI was designed to provide the public with information
about regional air quality and therefore it should be based on
community-wide monitors. These commenters went on to state that using
near-road NO2 monitors for the AQI would present problems
because they would not represent regional NO2 concentrations
and it would be difficult to communicate this type of information to
the public using the AQI. Some expressed concern that NO2
measured at near-roadway monitors could be the critical pollutant and
could drive the AQI even though it may not represent air quality across
the area. Other agencies expressed concern that there is currently no
way to forecast ambient NO2 levels near roadways. One State
agency commented that the AQI is intended to represent air quality
where people live, work and play.
EPA agrees with commenters that the AQI should represent regional
air quality, and that measurements that apply to a limited area should
not be used to characterize air quality across the region. Community-
wide NO2 monitors should be used to characterize air quality
across the region. However, the AQI reporting requirements encourage,
but do not require, the reporting of index values of sub-areas of an
MSA. We agree with the commenter that stated the view that the AQI is
intended to represent air quality where people live, work and play. To
the extent that near-roadway monitoring occurs in areas where people
live, work or play, EPA encourages reporting of the AQI for that
specific sub-area of the MSA (64 FR 42548, August 4, 1999). We also
agree that it may be difficult to communicate this type of information
and we plan to work with State and local air agencies to figure out the
best way to present this information to the public using the AQI. Air
quality forecasting is recommended but not required (64 FR 42548,
August 4, 1999). EPA will work with State agencies that want to develop
a forecasting program.
With regard to the proposed breakpoints, EPA received few comments.
The National Association of Clean Air Agencies commented that it would
be confusing to the public to have an AQI value of 50 set below the
level of the annual NO2 standard. We agree with this
comment, and therefore have decided that it is appropriate to set the
AQI value of 50, the breakpoint between the good and moderate ranges,
set at the numerical level of the annual standard, 53 ppb
NO2, 1-hour average. The AQI value of 100, the breakpoint
between the moderate and unhealthy for sensitive groups category, is
set at 100 ppb, 1-hour average, the level of the primary NO2
NAAQS. EPA is setting an AQI value of 150, the breakpoint between the
unhealthy for sensitive groups and unhealthy categories, at 0.360 ppm
NO2, 1-hour average.
VIII. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review
Under Executive Order 12866 (58 FR 51735, October 4, 1993), this
action is a ``significant regulatory action'' because it was deemed to
``raise novel legal or policy issues.'' Accordingly, EPA submitted this
action to the Office of Management and Budget (OMB) for review under
Executive Order 12866 and any changes made in response to OMB
recommendations have been documented in the docket for this action. In
addition, EPA prepared a Regulatory Impact Analysis (RIA) of the
potential costs and benefits associated with this action. However, the
CAA and judicial decisions make clear that the economic and technical
feasibility of attaining ambient standards are not to be considered in
setting or revising NAAQS, although such factors may be considered in
the development of State plans to implement the standards. Accordingly,
although an RIA has been prepared, the results of the RIA have not been
considered in developing this final rule.
B. Paperwork Reduction Act
The information collection requirements in this final rule have
been submitted for approval to the Office of Management and Budget
(OMB) under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. The
information collection requirements are not enforceable until OMB
approves them.
The Information Collection Request (ICR) document prepared by EPA
for these revisions to part 58 has been assigned EPA ICR number
2358.02.
The information collected under 40 CFR part 53 (e.g., test results,
monitoring records, instruction manual, and other associated
information) is needed to determine whether a candidate method intended
for use in determining attainment of the National Ambient Air Quality
Standards (NAAQS) in 40 CFR part 50 will meet
[[Page 6528]]
the design, performance, and/or comparability requirements for
designation as a Federal reference method (FRM) or Federal equivalent
method (FEM). We do not expect the number of FRM or FEM determinations
to increase over the number that is currently used to estimate burden
associated with NO2 FRM/FEM determinations provided in the
current ICR for 40 CFR part 53 (EPA ICR numbers 2358.01). As such, no
change in the burden estimate for 40 CFR part 53 has been made as part
of this rulemaking.
The information collected and reported under 40 CFR part 58 is
needed to determine compliance with the NAAQS, to characterize air
quality and associated health impacts, to develop emissions control
strategies, and to measure progress for the air pollution program. The
amendments would revise the technical requirements for NO2
monitoring sites, require the siting and operation of additional
NO2 ambient air monitors, and the reporting of the collected
ambient NO2 monitoring data to EPA's Air Quality System
(AQS). The annual average reporting burden for the collection under 40
CFR part 58 (averaged over the first 3 years of this ICR) is
$3,261,007. Burden is defined at 5 CFR 1320.3(b). State, local, and
Tribal entities are eligible for State assistance grants provided by
the Federal government under the CAA which can be used for monitors and
related activities.
An agency may not conduct or sponsor, and a person is not required
to respond to, a collection of information unless it displays a
currently valid OMB control number. The OMB control numbers for EPA's
regulations in 40 CFR are listed in 40 CFR part 9.
C. Regulatory Flexibility Act
The Regulatory Flexibility Act (RFA) generally requires an agency
to prepare a regulatory flexibility analysis of any rule subject to
notice and comment rulemaking requirements under the Administrative
Procedure Act or any other statute unless the agency certifies that the
rule will not have a significant economic impact on a substantial
number of small entities. Small entities include small businesses,
small organizations, and small governmental jurisdictions.
For purposes of assessing the impacts of this rule on small
entities, small entity is defined as: (1) A small business that is a
small industrial entity as defined by the Small Business
Administration's (SBA) regulations at 13 CFR 121.201; (2) a small
governmental jurisdiction that is a government of a city, county, town,
school district or special district with a population of less than
50,000; and (3) a small organization that is any not-for-profit
enterprise which is independently owned and operated and is not
dominant in its field.
After considering the economic impacts of this final rule on small
entities, I certify that this action will not have a significant
economic impact on a substantial number of small entities. This final
rule will not impose any requirements on small entities. Rather, this
rule establishes national standards for allowable concentrations of
NO2 in ambient air as required by section 109 of the CAA.
American Trucking Ass'ns v. EPA, 175 F.3d 1027, 1044-45 (DC cir. 1999)
(NAAQS do not have significant impacts upon small entities because
NAAQS themselves impose no regulations upon small entities). Similarly,
the amendments to 40 CFR part 58 address the requirements for States to
collect information and report compliance with the NAAQS and will not
impose any requirements on small entities.
D. Unfunded Mandates Reform Act
This rule does not contain a Federal mandate that may result in
expenditures of $100 million or more for State, local, and Tribal
governments, in the aggregate, or the private sector in any one year.
The revisions to the NO2 NAAQS impose no enforceable duty on
any State, local or Tribal governments or the private sector. The
expected costs associated with the monitoring requirements are
described in EPA's ICR document, but those costs are not expected to
exceed $100 million in the aggregate for any year. Furthermore, as
indicated previously, in setting a NAAQS EPA cannot consider the
economic or technological feasibility of attaining ambient air quality
standards. Because the Clean Air Act prohibits EPA from considering the
types of estimates and assessments described in section 202 when
setting the NAAQS, the UMRA does not require EPA to prepare a written
statement under section 202 for the revisions to the NO2
NAAQS. Thus, this rule is not subject to the requirements of sections
202 or 205 of UMRA.
With regard to implementation guidance, the CAA imposes the
obligation for States to submit SIPs to implement the NO2
NAAQS. In this final rule, EPA is merely providing an interpretation of
those requirements. However, even if this rule did establish an
independent obligation for States to submit SIPs, it is questionable
whether an obligation to submit a SIP revision would constitute a
Federal mandate in any case. The obligation for a State to submit a SIP
that arises out of section 110 and section 191 of the CAA is not
legally enforceable by a court of law, and at most is a condition for
continued receipt of highway funds. Therefore, it is possible to view
an action requiring such a submittal as not creating any enforceable
duty within the meaning of 2 U.S.C. 658 for purposes of the UMRA. Even
if it did, the duty could be viewed as falling within the exception for
a condition of Federal assistance under 2 U.S.C. 658.
This rule is also not subject to the requirements of section 203 of
UMRA because it contains no regulatory requirements that might
significantly or uniquely affect small governments because it imposes
no enforceable duty on any small governments.
E. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have
substantial direct effects on the States, on the relationship between
the national government and the States, or on the distribution of power
and responsibilities among the various levels of government, as
specified in Executive Order 13132. The rule does not alter the
relationship between the Federal government and the States regarding
the establishment and implementation of air quality improvement
programs as codified in the CAA. Under section 109 of the CAA, EPA is
mandated to establish NAAQS; however, CAA section 116 preserves the
rights of States to establish more stringent requirements if deemed
necessary by a State. Furthermore, this rule does not impact CAA
section 107 which establishes that the States have primary
responsibility for implementation of the NAAQS. Finally, as noted in
section E (above) on UMRA, this rule does not impose significant costs
on State, local, or Tribal governments or the private sector. Thus,
Executive Order 13132 does not apply to this rule.
F. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments
This action does not have Tribal implications, as specified in
Executive Order 13175 (65 FR 67249, November 9, 2000). It does not have
a substantial direct effect on one or more Indian Tribes, on the
relationship between the Federal government and Indian Tribes, or on
the distribution of power and responsibilities between the Federal
government and Tribes. The rule does not alter the relationship between
the
[[Page 6529]]
Federal government and Tribes as established in the CAA and the TAR.
Under section 109 of the CAA, EPA is mandated to establish NAAQS;
however, this rule does not infringe existing Tribal authorities to
regulate air quality under their own programs or under programs
submitted to EPA for approval. Furthermore, this rule does not affect
the flexibility afforded to Tribes in seeking to implement CAA programs
consistent with the TAR, nor does it impose any new obligation on
Tribes to adopt or implement any NAAQS. Finally, as noted in section E
(above) on UMRA, this rule does not impose significant costs on Tribal
governments. Thus, Executive Order 13175 does not apply to this action.
G. Executive Order 13045: Protection of Children From Environmental
Health Risks and Safety Risks
This action is subject to Executive Order 13045 (62 FR 19885, April
23, 1997) because it is an economically significant regulatory action
as defined by Executive Order 12866, and EPA believes that the
environmental health or safety risk addressed by this action has a
disproportionate effect on children. The final rule will establish
uniform national ambient air quality standards for NO2;
these standards are designed to protect public health with an adequate
margin of safety, as required by CAA section 109. The protection
offered by these standards may be especially important for asthmatics,
including asthmatic children, because respiratory effects in asthmatics
are among the most sensitive health endpoints for NO2
exposure. Because asthmatic children are considered a sensitive
population, we have evaluated the potential health effects of exposure
to NO2 pollution among asthmatic children. These effects and
the size of the population affected are discussed in chapters 3 and 4
of the ISA; chapters 3, 4, and 8 of the REA, and sections II.A through
II.E of this preamble.
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution or Use
This action is not a ``significant energy action'' as defined in
Executive Order 13211, ``Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use'' (66 FR 28355
(May 22, 2001)) because it is not likely to have a significant adverse
effect on the supply, distribution, or use of energy. The purpose of
this rule is to establish revised NAAQS for NO2. The rule
does not prescribe specific control strategies by which these ambient
standards will be met. Such strategies will be developed by States on a
case-by-case basis, and EPA cannot predict whether the control options
selected by States will include regulations on energy suppliers,
distributors, or users. Thus, EPA concludes that this rule is not
likely to have any adverse energy effects.
I. National Technology Transfer and Advancement Act
Section 12(d) of the National Technology Transfer and Advancement
Act of 1995 (NTTAA), Public Law 104-113, section 12(d) (15 U.S.C.
272 note) directs EPA to use voluntary consensus standards
in its regulatory activities unless to do so would be inconsistent with
applicable law or otherwise impractical. Voluntary consensus standards
are technical standards (e.g., materials specifications, test methods,
sampling procedures, and business practices) that are developed or
adopted by voluntary consensus standards bodies. The NTTAA directs EPA
to provide Congress, through OMB, explanations when the Agency decides
not to use available and applicable voluntary consensus standards.
This final rulemaking involves technical standards. Therefore the
Agency conducted a search to identify potential applicable voluntary
consensus standards. However, we identified no such standards, and none
were brought to our attention in comments. Therefore, EPA has decided
to use the technical standard described in Section III.A of the
preamble.
J. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations
Executive Order 12898 (59 FR 7629; Feb. 16, 1994) establishes
Federal executive policy on environmental justice. Its main provision
directs Federal agencies, to the greatest extent practicable and
permitted by law, to make environmental justice part of their mission
by identifying and addressing, as appropriate, disproportionately high
and adverse human health or environmental effects of their programs,
policies, and activities on minority populations and low-income
populations in the United States.
EPA has determined that this final rule will not have
disproportionately high and adverse human health or environmental
effects on minority or low-income populations because it increases the
level of environmental protection for all affected populations without
having any disproportionately high and adverse human health effects on
any population, including any minority or low-income population. The
final rule will establish uniform national standards for NO2
in ambient air.
K. Congressional Review Act
The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the
Small Business Regulatory Enforcement Fairness Act of 1996, generally
provides that before a rule may take effect, the agency promulgating
the rule must submit a rule report, which includes a copy of the rule,
to each House of the Congress and to the Comptroller General of the
United States. EPA will submit a report containing this rule and other
required information to the U.S. Senate, the U.S. House of
Representatives, and the Comptroller General of the United States prior
to publication of the rule in the Federal Register. A Major rule cannot
take effect until 60 days after it is published in the Federal
Register. This action is a ``major rule'' as defined by 5 U.S.C.
804(2). This rule will be effective on April 12, 2010.
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[[Page 6531]]
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List of Subjects
40 CFR Part 50
Environmental protection, Air pollution control, Carbon monoxide,
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.
40 CFR Part 58
Environmental protection, Administrative practice and procedure,
Air pollution control, Intergovernmental relations, Reporting and
recordkeeping requirements.
Dated: January 22, 2010.
Lisa P. Jackson,
Administrator.
0
For the reasons stated in the preamble, title 40, chapter I of the Code
of Federal Regulations is amended as follows:
PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY
STANDARDS
0
1. The authority citation for part 50 continues to read as follows:
Authority: 42 U.S.C. 7401, et seq.
0
2. Section 50.11 is revised to read as follows:
Sec. 50.11 National primary and secondary ambient air quality
standards for oxides of nitrogen (with nitrogen dioxide as the
indicator).
(a) The level of the national primary annual ambient air quality
standard for oxides of nitrogen is 53 parts per billion (ppb, which is
1 part in 1,000,000,000), annual average concentration, measured in the
ambient air as nitrogen dioxide.
(b) The level of the national primary 1-hour ambient air quality
standard for oxides of nitrogen is 100 ppb, 1-hour average
concentration, measured in the ambient air as nitrogen dioxide.
(c) The level of the national secondary ambient air quality
standard for nitrogen dioxide is 0.053 parts per million (100
micrograms per cubic meter), annual arithmetic mean concentration.
(d) The levels of the standards shall be measured by:
(1) A reference method based on appendix F to this part; or
(2) By a Federal equivalent method (FEM) designated in accordance
with part 53 of this chapter.
(e) The annual primary standard is met when the annual average
concentration in a calendar year is less than or equal to 53 ppb, as
determined in accordance with Appendix S of this part for the annual
standard.
(f) The 1-hour primary standard is met when the three-year average
of the annual 98th percentile of the daily maximum 1-hour average
concentration is less than or equal to 100 ppb, as determined in
accordance with Appendix S of this part for the 1-hour standard.
(g) The secondary standard is attained when the annual arithmetic
mean concentration in a calendar year is less than or equal to 0.053
ppm, rounded to three decimal places (fractional parts equal to or
greater than 0.0005 ppm must be rounded up). To demonstrate attainment,
an annual mean must be based upon hourly data that are at least 75
percent complete or upon data derived from manual methods that are at
least 75 percent complete for the scheduled sampling days in each
calendar quarter.
0
3. Section 50.14 is amended by adding an entry to the end of table in
paragraph (c)(2)(vi) to read as follows:
Sec. 50.14 Treatment of air quality monitoring data influenced by
exceptional events.
* * * * *
(c) * * *
(2) * * *
(vi) * * *
Table 1--Schedule for Exceptional Event Flagging and Documentation Submission for Data To Be Used in
Designations Decisions for New or Revised NAAQS
----------------------------------------------------------------------------------------------------------------
Air quality
NAAQS pollutant/ standard/ (level)/ data collected Event flagging & initial Detailed documentation
promulgation date for calendar description deadline submission deadline
year
----------------------------------------------------------------------------------------------------------------
* * * * * * *
NO2/1-Hour Standard (100 PPB)........ 2008 July 1, 2010 \a\........ January 22, 2011.
2009 July 1, 2010............ January 22, 2011.
2010 April 1, 2011 \a\....... July 1, 2011 \a\.
----------------------------------------------------------------------------------------------------------------
\a\ Indicates change from general schedule in 40 CFR 50.14.
Note: EPA notes that the table of revised deadlines only applies to data EPA will use to establish the final
initial designations for new or revised NAAQS. The general schedule applies for all other purposes, most
notably, for data used by EPA for redesignations to attainment.
[[Page 6532]]
* * * * *
0
4. Appendix S to Part 50 is added to read as follows:
Appendix S to Part 50--Interpretation of the Primary National Ambient
Air Quality Standards for Oxides of Nitrogen (Nitrogen Dioxide)
1. General
(a) This appendix explains the data handling conventions and
computations necessary for determining when the primary national
ambient air quality standards for oxides of nitrogen as measured by
nitrogen dioxide (``NO2 NAAQS'') specified in 50.11 are
met. Nitrogen dioxide (NO2) is measured in the ambient
air by a Federal reference method (FRM) based on appendix F to this
part or by a Federal equivalent method (FEM) designated in
accordance with part 53 of this chapter. Data handling and
computation procedures to be used in making comparisons between
reported NO2 concentrations and the levels of the
NO2 NAAQS are specified in the following sections.
(b) Whether to exclude, retain, or make adjustments to the data
affected by exceptional events, including natural events, is
determined by the requirements and process deadlines specified in
50.1, 50.14 and 51.930 of this chapter.
(c) The terms used in this appendix are defined as follows:
Annual mean refers to the annual average of all of the 1-hour
concentration values as defined in section 5.1 of this appendix.
Daily maximum 1-hour values for NO2 refers to the
maximum 1-hour NO2 concentration values measured from
midnight to midnight (local standard time) that are used in NAAQS
computations.
Design values are the metrics (i.e., statistics) that are
compared to the NAAQS levels to determine compliance, calculated as
specified in section 5 of this appendix. The design values for the
primary NAAQS are:
(1) The annual mean value for a monitoring site for one year
(referred to as the ``annual primary standard design value'').
(2) The 3-year average of annual 98th percentile daily maximum
1-hour values for a monitoring site (referred to as the ``1-hour
primary standard design value'').
98th percentile daily maximum 1-hour value is the value below
which nominally 98 percent of all daily maximum 1-hour concentration
values fall, using the ranking and selection method specified in
section 5.2 of this appendix.
Quarter refers to a calendar quarter.
Year refers to a calendar year.
2. Requirements for Data Used for Comparisons With the NO2
NAAQS and Data Reporting Considerations
(a) All valid FRM/FEM NO2 hourly data required to be
submitted to EPA's Air Quality System (AQS), or otherwise available
to EPA, meeting the requirements of part 58 of this chapter
including appendices A, C, and E shall be used in design value
calculations. Multi-hour average concentration values collected by
wet chemistry methods shall not be used.
(b) When two or more NO2 monitors are operated at a
site, the State may in advance designate one of them as the primary
monitor. If the State has not made this designation, the
Administrator will make the designation, either in advance or
retrospectively. Design values will be developed using only the data
from the primary monitor, if this results in a valid design value.
If data from the primary monitor do not allow the development of a
valid design value, data solely from the other monitor(s) will be
used in turn to develop a valid design value, if this results in a
valid design value. If there are three or more monitors, the order
for such comparison of the other monitors will be determined by the
Administrator. The Administrator may combine data from different
monitors in different years for the purpose of developing a valid 1-
hour primary standard design value, if a valid design value cannot
be developed solely with the data from a single monitor. However,
data from two or more monitors in the same year at the same site
will not be combined in an attempt to meet data completeness
requirements, except if one monitor has physically replaced another
instrument permanently, in which case the two instruments will be
considered to be the same monitor, or if the State has switched the
designation of the primary monitor from one instrument to another
during the year.
(c) Hourly NO2 measurement data shall be reported to
AQS in units of parts per billion (ppb), to at most one place after
the decimal, with additional digits to the right being truncated
with no further rounding.
3. Comparisons With the NO2 NAAQS
3.1 The Annual Primary NO2 NAAQS
(a) The annual primary NO2 NAAQS is met at a site
when the valid annual primary standard design value is less than or
equal to 53 parts per billion (ppb).
(b) An annual primary standard design value is valid when at
least 75 percent of the hours in the year are reported.
(c) An annual primary standard design value based on data that
do not meet the completeness criteria stated in section 3.1(b) may
also be considered valid with the approval of, or at the initiative
of, the Administrator, who may consider factors such as monitoring
site closures/moves, monitoring diligence, the consistency and
levels of the valid concentration measurements that are available,
and nearby concentrations in determining whether to use such data.
(d) The procedures for calculating the annual primary standard
design values are given in section 5.1 of this appendix.
3.2 The 1-hour Primary NO2 NAAQS
(a) The 1-hour primary NO2 NAAQS is met at a site
when the valid 1-hour primary standard design value is less than or
equal to 100 parts per billion (ppb).
(b) An NO2 1-hour primary standard design value is
valid if it encompasses three consecutive calendar years of complete
data. A year meets data completeness requirements when all 4
quarters are complete. A quarter is complete when at least 75
percent of the sampling days for each quarter have complete data. A
sampling day has complete data if 75 percent of the hourly
concentration values, including State-flagged data affected by
exceptional events which have been approved for exclusion by the
Administrator, are reported.
(c) In the case of one, two, or three years that do not meet the
completeness requirements of section 3.2(b) of this appendix and
thus would normally not be useable for the calculation of a valid 3-
year 1-hour primary standard design value, the 3-year 1-hour primary
standard design value shall nevertheless be considered valid if one
of the following conditions is true.
(i) At least 75 percent of the days in each quarter of each of
three consecutive years have at least one reported hourly value, and
the design value calculated according to the procedures specified in
section 5.2 is above the level of the primary 1-hour standard.
(ii)(A) A 1-hour primary standard design value that is below the
level of the NAAQS can be validated if the substitution test in
section 3.2(c)(ii)(B) results in a ``test design value'' that is
below the level of the NAAQS. The test substitutes actual ``high''
reported daily maximum 1-hour values from the same site at about the
same time of the year (specifically, in the same calendar quarter)
for unknown values that were not successfully measured. Note that
the test is merely diagnostic in nature, intended to confirm that
there is a very high likelihood that the original design value (the
one with less than 75 percent data capture of hours by day and of
days by quarter) reflects the true under-NAAQS-level status for that
3-year period; the result of this data substitution test (the ``test
design value'', as defined in section 3.2(c)(ii)(B)) is not
considered the actual design value. For this test, substitution is
permitted only if there are at least 200 days across the three
matching quarters of the three years under consideration (which is
about 75 percent of all possible daily values in those three
quarters) for which 75 percent of the hours in the day, including
State-flagged data affected by exceptional events which have been
approved for exclusion by the Administrator, have reported
concentrations. However, maximum 1-hour values from days with less
than 75 percent of the hours reported shall also be considered in
identifying the high value to be used for substitution.
(B) The substitution test is as follows: Data substitution will
be performed in all quarter periods that have less than 75 percent
data capture but at least 50 percent data capture, including State-
flagged data affected by exceptional events which have been approved
for exclusion by the Administrator; if any quarter has less than 50
percent data capture then this substitution test cannot be used.
Identify for each quarter (e.g., January-March) the highest reported
daily maximum 1-hour value for that quarter, excluding State-flagged
data affected by exceptional events which have been approved for
exclusion by the Administrator, looking across those three months of
all three years under consideration. All daily maximum 1-hour values
from all days in the quarter period shall be considered when
identifying this highest value, including days with less than
[[Page 6533]]
75 percent data capture. If after substituting the highest non-
excluded reported daily maximum 1-hour value for a quarter for as
much of the missing daily data in the matching deficient quarter(s)
as is needed to make them 100 percent complete, the procedure in
section 5.2 yields a recalculated 3-year 1-hour standard ``test
design value'' below the level of the standard, then the 1-hour
primary standard design value is deemed to have passed the
diagnostic test and is valid, and the level of the standard is
deemed to have been met in that 3-year period. As noted in section
3.2(c)(i), in such a case, the 3-year design value based on the data
actually reported, not the ``test design value'', shall be used as
the valid design value.
(iii)(A) A 1-hour primary standard design value that is above
the level of the NAAQS can be validated if the substitution test in
section 3.2(c)(iii)(B) results in a ``test design value'' that is
above the level of the NAAQS. The test substitutes actual ``low''
reported daily maximum 1-hour values from the same site at about the
same time of the year (specifically, in the same three months of the
calendar) for unknown values that were not successfully measured.
Note that the test is merely diagnostic in nature, intended to
confirm that there is a very high likelihood that the original
design value (the one with less than 75 percent data capture of
hours by day and of days by quarter) reflects the true above-NAAQS-
level status for that 3-year period; the result of this data
substitution test (the ``test design value'', as defined in section
3.2(c)(iii)(B)) is not considered the actual design value. For this
test, substitution is permitted only if there are a minimum number
of available daily data points from which to identify the low
quarter-specific daily maximum 1-hour values, specifically if there
are at least 200 days across the three matching quarters of the
three years under consideration (which is about 75 percent of all
possible daily values in those three quarters) for which 75 percent
of the hours in the day have reported concentrations. Only days with
at least 75 percent of the hours reported shall be considered in
identifying the low value to be used for substitution.
(B) The substitution test is as follows: Data substitution will
be performed in all quarter periods that have less than 75 percent
data capture. Identify for each quarter (e.g., January-March) the
lowest reported daily maximum 1-hour value for that quarter, looking
across those three months of all three years under consideration.
All daily maximum 1-hour values from all days with at least 75
percent capture in the quarter period shall be considered when
identifying this lowest value. If after substituting the lowest
reported daily maximum 1-hour value for a quarter for as much of the
missing daily data in the matching deficient quarter(s) as is needed
to make them 75 percent complete, the procedure in section 5.2
yields a recalculated 3-year 1-hour standard ``test design value''
above the level of the standard, then the 1-hour primary standard
design value is deemed to have passed the diagnostic test and is
valid, and the level of the standard is deemed to have been exceeded
in that 3-year period. As noted in section 3.2(c)(i), in such a
case, the 3-year design value based on the data actually reported,
not the ``test design value'', shall be used as the valid design
value.
(d) A 1-hour primary standard design value based on data that do
not meet the completeness criteria stated in 3.2(b) and also do not
satisfy section 3.2(c), may also be considered valid with the
approval of, or at the initiative of, the Administrator, who may
consider factors such as monitoring site closures/moves, monitoring
diligence, the consistency and levels of the valid concentration
measurements that are available, and nearby concentrations in
determining whether to use such data.
(e) The procedures for calculating the 1-hour primary standard
design values are given in section 5.2 of this appendix.
4. Rounding Conventions
4.1 Rounding Conventions for the Annual Primary NO2
NAAQS
(a) Hourly NO2 measurement data shall be reported to
AQS in units of parts per billion (ppb), to at most one place after
the decimal, with additional digits to the right being truncated
with no further rounding.
(b) The annual primary standard design value is calculated
pursuant to section 5.1 and then rounded to the nearest whole number
or 1 ppb (decimals 0.5 and greater are rounded up to the nearest
whole number, and any decimal lower than 0.5 is rounded down to the
nearest whole number).
4.2 Rounding Conventions for the 1-hour Primary NO2 NAAQS
(a) Hourly NO2 measurement data shall be reported to
AQS in units of parts per billion (ppb), to at most one place after
the decimal, with additional digits to the right being truncated
with no further rounding.
(b) Daily maximum 1-hour values are not rounded.
(c) The 1-hour primary standard design value is calculated
pursuant to section 5.2 and then rounded to the nearest whole number
or 1 ppb (decimals 0.5 and greater are rounded up to the nearest
whole number, and any decimal lower than 0.5 is rounded down to the
nearest whole number).
5. Calculation Procedures for the Primary NO2 NAAQS
5.1 Procedures for the Annual Primary NO2 NAAQS
(a) When the data for a site and year meet the data completeness
requirements in section 3.1(b) of this appendix, or if the
Administrator exercises the discretionary authority in section
3.1(c), the annual mean is simply the arithmetic average of all of
the reported 1-hour values.
(b) The annual primary standard design value for a site is the
valid annual mean rounded according to the conventions in section
4.1.
5.2 Calculation Procedures for the 1-hour Primary NO2 NAAQS
(a) Procedure for identifying annual 98th percentile values.
When the data for a particular site and year meet the data
completeness requirements in section 3.2(b), or if one of the
conditions of section 3.2(c) is met, or if the Administrator
exercises the discretionary authority in section 3.2(d),
identification of annual 98th percentile value is accomplished as
follows.
(i) The annual 98th percentile value for a year is the higher of
the two values resulting from the following two procedures.
(1) Procedure 1.
(A) For the year, determine the number of days with at least 75
percent of the hourly values reported including State-flagged data
affected by exceptional events which have been approved for
exclusion by the Administrator.
(B) For the year, from only the days with at least 75 percent of
the hourly values reported, select from each day the maximum hourly
value excluding State-flagged data affected by exceptional events
which have been approved for exclusion by the Administrator.
(C) Sort all these daily maximum hourly values from a particular
site and year by descending value. (For example: (x[1], x[2], x[3],
* * *, x[n]). In this case, x[1] is the largest number and x[n] is
the smallest value.) The 98th percentile is determined from this
sorted series of daily values which is ordered from the highest to
the lowest number. Using the left column of Table 1, determine the
appropriate range (i.e., row) for the annual number of days with
valid data for year y (cny) as determined from step (A).
The corresponding ``n'' value in the right column identifies the
rank of the annual 98th percentile value in the descending sorted
list of daily site values for year y. Thus, P0.98, y =
the nth largest value.
(2) Procedure 2.
(A) For the year, determine the number of days with at least one
hourly value reported including State-flagged data affected by
exceptional events which have been approved for exclusion by the
Administrator.
(B) For the year, from all the days with at least one hourly
value reported, select from each day the maximum hourly value
excluding State-flagged data affected by exceptional events which
have been approved for exclusion by the Administrator.
(C) Sort all these daily maximum values from a particular site
and year by descending value. (For example: (x[1], x[2], x[3], * *
*, x[n]). In this case, x[1] is the largest number and x[n] is the
smallest value.) The 98th percentile is determined from this sorted
series of daily values which is ordered from the highest to the
lowest number. Using the left column of Table 1, determine the
appropriate range (i.e., row) for the annual number of days with
valid data for year y (cny) as determined from step (A).
The corresponding ``n'' value in the right column identifies the
rank of the annual 98th percentile value in the descending sorted
list of daily site values for year y. Thus, P0.98, y =
the nth largest value.
(b) The 1-hour primary standard design value for a site is mean
of the three annual 98th percentile values, rounded according to the
conventions in section 4.
[[Page 6534]]
Table 1
------------------------------------------------------------------------
P0.98, y is the
nth maximum value
Annual number of days with valid data for year of the year,
``y'' (cny) where n is the
listed number
------------------------------------------------------------------------
1-50................................................ 1
51-100.............................................. 2
101-150............................................. 3
151-200............................................. 4
201-250............................................. 5
251-300............................................. 6
301-350............................................. 7
351-366............................................. 8
------------------------------------------------------------------------
PART 58--AMBIENT AIR QUALITY SURVEILLANCE
0
5. The authority citation for part 58 continues to read as follows:
Authority: 42 U.S.C. 7403, 7410, 7601(a), 7611, and 7619.
Subpart A--[Amended]
0
6. Section 58.1, is amended by adding the definitions for ``AADT'' and
``Near-road NO2 Monitor'' in alphabetical order to read as
follows:
Sec. 58.1 Definitions
* * * * *
AADT means the annual average daily traffic.
* * *
Near-road NO2 Monitor means any NO2 monitor meeting the
specifications in 4.3.2 of Appendix D and paragraphs 2, 4(d), 6.1, and
6.4 of Appendix E of this part.
* * * * *
Subpart B [Amended]
0
7. Section 58.10, is amended by adding paragraphs (a)(5) and (b)(12) to
read as follows:
Sec. 58.10 Annual monitoring network plan and periodic network
assessment.
(a) * * *
(5) A plan for establishing NO2 monitoring sites in
accordance with the requirements of appendix D to this part shall be
submitted to the Administrator by July 1, 2012. The plan shall provide
for all required monitoring stations to be operational by January 1,
2013.
* * * * *
(b) * * *
(12) The identification of required NO2 monitors as
either near-road or area-wide sites in accordance with Appendix D,
Section 4.3 of this part.
* * * * *
0
8. Section 58.13 is amended by adding paragraph (c) to read as follows:
Sec. 58.13 Monitoring network completion.
* * * * *
(c) The network of NO2 monitors must be physically
established no later than January 1, 2013, and at that time, must be
operating under all of the requirements of this part, including the
requirements of appendices A, C, D, and E to this part.
0
9. Section 58.16 is amended by revising paragraph (a) to read as
follows:
Sec. 58.16 Data submittal and archiving requirements.
* * * * *
(a) The State, or where appropriate, local agency, shall report to
the Administrator, via AQS all ambient air quality data and associated
quality assurance data for SO2; CO; O3;
NO2; NO; NOY; NOX; Pb-TSP mass
concentration; Pb-PM10 mass concentration; PM10
mass concentration; PM2.5mass concentration; for filter-
based PM2.5FRM/FEM the field blank mass, sampler-generated
average daily temperature, and sampler-generated average daily
pressure; chemically speciated PM2.5 mass concentration
data; PM10-2.5 mass concentration; chemically speciated
PM10-2.5 mass concentration data; meteorological data from
NCore and PAMS sites; average daily temperature and average daily
pressure for Pb sites if not already reported from sampler generated
records; and metadata records and information specified by the AQS Data
Coding Manual (http://www.epa.gov/ttn/airs/airsaqs/manuals/manuals.htm). The State, or where appropriate, local agency, may report
site specific meteorological measurements generated by onsite equipment
(meteorological instruments, or sampler generated) or measurements from
the nearest airport reporting ambient pressure and temperature. Such
air quality data and information must be submitted directly to the AQS
via electronic transmission on the specified quarterly schedule
described in paragraph (b) of this section.
* * * * *
0
10. Appendix A to Part 58 is amended by adding paragraph 2.3.1.5 to
read as follows:
Appendix A to Part 58--Quality Assurance Requirements for SLAMS, SPMs
and PSD Air Monitoring
* * * * *
2.3.1.5 Measurement Uncertainty for NO2. The goal for
acceptable measurement uncertainty is defined for precision as an
upper 90 percent confidence limit for the coefficient of variation
(CV) of 15 percent and for bias as an upper 95 percent confidence
limit for the absolute bias of 15 percent.
* * * * *
0
11. Appendix C to Part 58 is amended by adding paragraph 2.1.1 to read
as follows:
Appendix C to Part 58--Ambient Air Quality Monitoring Methodology
* * * * *
2.1.1 Any NO2 FRM or FEM used for making primary
NAAQS decisions must be capable of providing hourly averaged
concentration data.
* * * * *
0
12. Appendix D to Part 58 is amended by revising paragraph 4.3 to read
as follows:
Appendix D to Part 58--Network Design Criteria for Ambient Air Quality
Monitoring
* * * * *
4.3 Nitrogen Dioxide (NO2) Design Criteria
4.3.1 General Requirements
(a) State and, where appropriate, local agencies must operate a
minimum number of required NO2 monitoring sites as
described below.
4.3.2 Requirement for Near-road NO2 Monitors
(a) Within the NO2 network, there must be one
microscale near-road NO2 monitoring station in each CBSA
with a population of 500,000 or more persons to monitor a location
of expected maximum hourly concentrations sited near a major road
with high AADT counts as specified in paragraph 4.3.2(a)(1) of this
appendix. An additional near-road NO2 monitoring station
is required for any CBSA with a population of 2,500,000 persons or
more, or in any CBSA with a population of 500,000 or more persons
that has one or more roadway segments with 250,000 or greater AADT
counts to monitor a second location of expected maximum hourly
concentrations. CBSA populations shall be based on the latest
available census figures.
(1) The near-road NO2 monitoring stations shall be
selected by ranking all road segments within a CBSA by AADT and then
identifying a location or locations adjacent to those highest ranked
road segments, considering fleet mix, roadway design, congestion
patterns, terrain, and meteorology, where maximum hourly
NO2 concentrations are expected to occur and siting
criteria can be met in accordance with appendix E of this part.
Where a State or local air monitoring agency identifies multiple
acceptable candidate sites where maximum hourly NO2
concentrations are expected to occur, the monitoring agency shall
consider the potential for population exposure in the criteria
utilized to select the final site location. Where one CBSA is
required to have two near-road NO2 monitoring stations,
the sites shall be differentiated from each other by one or more of
the following factors: fleet mix; congestion patterns; terrain;
geographic area within the
[[Page 6535]]
CBSA; or different route, interstate, or freeway designation.
(b) Measurements at required near-road NO2 monitor
sites utilizing chemiluminescence FRMs must include at a minimum:
NO, NO2, and NOX.
4.3.3 Requirement for Area-wide NO2 Monitoring
(a) Within the NO2 network, there must be one
monitoring station in each CBSA with a population of 1,000,000 or
more persons to monitor a location of expected highest
NO2 concentrations representing the neighborhood or
larger spatial scales. PAMS sites collecting NO2 data
that are situated in an area of expected high NO2
concentrations at the neighborhood or larger spatial scale may be
used to satisfy this minimum monitoring requirement when the
NO2 monitor is operated year round. Emission inventories
and meteorological analysis should be used to identify the
appropriate locations within a CBSA for locating required area-wide
NO2 monitoring stations. CBSA populations shall be based
on the latest available census figures.
4.3.4 Regional Administrator Required Monitoring
(a) The Regional Administrators, in collaboration with States,
must require a minimum of forty additional NO2 monitoring
stations nationwide in any area, inside or outside of CBSAs, above
the minimum monitoring requirements, with a primary focus on siting
these monitors in locations to protect susceptible and vulnerable
populations. The Regional Administrators, working with States, may
also consider additional factors described in paragraph (b) below to
require monitors beyond the minimum network requirement.
(b) The Regional Administrators may require monitors to be sited
inside or outside of CBSAs in which:
(i) The required near-road monitors do not represent all
locations of expected maximum hourly NO2 concentrations
in an area and NO2 concentrations may be approaching or
exceeding the NAAQS in that area;
(ii) Areas that are not required to have a monitor in accordance
with the monitoring requirements and NO2 concentrations
may be approaching or exceeding the NAAQS; or
(iii) The minimum monitoring requirements for area-wide monitors
are not sufficient to meet monitoring objectives.
(c) The Regional Administrator and the responsible State or
local air monitoring agency should work together to design and/or
maintain the most appropriate NO2 network to address the
data needs for an area, and include all monitors under this
provision in the annual monitoring network plan.
4.3.5 NO2 Monitoring Spatial Scales
(a) The most important spatial scale for near-road
NO2 monitoring stations to effectively characterize the
maximum expected hourly NO2 concentration due to mobile
source emissions on major roadways is the microscale. The most
important spatial scales for other monitoring stations
characterizing maximum expected hourly NO2 concentrations
are the microscale and middle scale. The most important spatial
scale for area-wide monitoring of high NO2 concentrations
is the neighborhood scale.
(1) Microscale--This scale represents areas in close proximity
to major roadways or point and area sources. Emissions from roadways
result in high ground level NO2 concentrations at the
microscale, where concentration gradients generally exhibit a marked
decrease with increasing downwind distance from major roads. As
noted in appendix E of this part, near-road NO2
monitoring stations are required to be within 50 meters of target
road segments in order to measure expected peak concentrations.
Emissions from stationary point and area sources, and non-road
sources may, under certain plume conditions, result in high ground
level concentrations at the microscale. The microscale typically
represents an area impacted by the plume with dimensions extending
up to approximately 100 meters.
(2) Middle scale--This scale generally represents air quality
levels in areas up to several city blocks in size with dimensions on
the order of approximately 100 meters to 500 meters. The middle
scale may include locations of expected maximum hourly
concentrations due to proximity to major NO2 point, area,
and/or non-road sources.
(3) Neighborhood scale--The neighborhood scale represents air
quality conditions throughout some relatively uniform land use areas
with dimensions in the 0.5 to 4.0 kilometer range. Emissions from
stationary point and area sources may, under certain plume
conditions, result in high NO2 concentrations at the
neighborhood scale. Where a neighborhood site is located away from
immediate NO2 sources, the site may be useful in
representing typical air quality values for a larger residential
area, and therefore suitable for population exposure and trends
analyses.
(4) Urban scale--Measurements in this scale would be used to
estimate concentrations over large portions of an urban area with
dimensions from 4 to 50 kilometers. Such measurements would be
useful for assessing trends in area-wide air quality, and hence, the
effectiveness of large scale air pollution control strategies. Urban
scale sites may also support other monitoring objectives of the
NO2 monitoring network identified in paragraph 4.3.4
above.
4.3.6 NOy Monitoring
(a) NO/NOy measurements are included within the NCore
multi-pollutant site requirements and the PAMS program. These NO/
NOy measurements will produce conservative estimates for
NO2 that can be used to ensure tracking continued
compliance with the NO2 NAAQS. NO/NOy monitors
are used at these sites because it is important to collect data on
total reactive nitrogen species for understanding O3
photochemistry.
* * * * *
0
13. Appendix E to Part 58 is amended as follows:
0
a. By revising paragraphs 2, and 6.1.
0
b. By adding paragraphs 4(d) and 6.4.
0
c. By revising paragraphs 9(c), 11 and Table E-4.
Appendix E to Part 58--Probe and Monitoring Path Siting Criteria for
Ambient Air Quality Monitoring
* * * * *
2. Horizontal and Vertical Placement
The probe or at least 80 percent of the monitoring path must be
located between 2 and 15 meters above ground level for all ozone and
sulfur dioxide monitoring sites, and for neighborhood or larger
spatial scale Pb, PM10, PM10-2.5,
PM2.5, NO2 and carbon monoxide sites. Middle
scale PM10-2.5 sites are required to have sampler inlets
between 2 and 7 meters above ground level. Microscale Pb,
PM10, PM10-2.5 and PM2.5 sites are
required to have sampler inlets between 2 and 7 meters above ground
level. Microscale near-road NO2 monitoring sites are
required to have sampler inlets between 2 and 7 meters above ground
level. The inlet probes for microscale carbon monoxide monitors that
are being used to measure concentrations near roadways must be
3\1/2\ meters above ground level. The probe or at least
90 percent of the monitoring path must be at least 1 meter
vertically or horizontally away from any supporting structure,
walls, parapets, penthouses, etc., and away from dusty or dirty
areas. If the probe or a significant portion of the monitoring path
is located near the side of a building or wall, then it should be
located on the windward side of the building relative to the
prevailing wind direction during the season of highest concentration
potential for the pollutant being measured.
* * * * *
4. * * *
(d) For near-road NO2 monitoring stations, the
monitor probe shall have an unobstructed air flow, where no
obstacles exist at or above the height of the monitor probe, between
the monitor probe and the outside nearest edge of the traffic lanes
of the target road segment.
* * * * *
6. * * *
6.1 Spacing for Ozone Probes and Monitoring Paths
In siting an O3 analyzer, it is important to minimize
destructive interferences form sources of NO, since NO readily
reacts with O3. Table E-1 of this appendix provides the
required minimum separation distances between a roadway and a probe
or, where applicable, at least 90 percent of a monitoring path for
various ranges of daily roadway traffic. A sampling site having a
point analyzer probe located closer to a roadway than allowed by the
Table E-1 requirements should be classified as microscale or middle
scale, rather than neighborhood or urban scale, since the
measurements from such a site would more closely represent the
middle scale. If an open path analyzer is used at a site, the
monitoring path(s) must not cross over a roadway with an average
daily traffic count of 10,000 vehicles per day or more. For those
situations where a monitoring path crosses a roadway with fewer than
10,000 vehicles per day, monitoring agencies must consider the
entire segment of the monitoring
[[Page 6536]]
path in the area of potential atmospheric interference from
automobile emissions. Therefore, this calculation must include the
length of the monitoring path over the roadway plus any segments of
the monitoring path that lie in the area between the roadway and
minimum separation distance, as determined from the Table E-1 of
this appendix. The sum of these distances must not be greater than
10 percent of the total monitoring path length.
* * * * *
6.4 Spacing for Nitrogen Dioxide (NO2) Probes and
Monitoring Paths
(a) In siting near-road NO2 monitors as required in
paragraph 4.3.2 of appendix D of this part, the monitor probe shall
be as near as practicable to the outside nearest edge of the traffic
lanes of the target road segment; but shall not be located at a
distance greater than 50 meters, in the horizontal, from the outside
nearest edge of the traffic lanes of the target road segment.
(b) In siting NO2 monitors for neighborhood and
larger scale monitoring, it is important to minimize near-road
influences. Table E-1 of this appendix provides the required minimum
separation distances between a roadway and a probe or, where
applicable, at least 90 percent of a monitoring path for various
ranges of daily roadway traffic. A sampling site having a point
analyzer probe located closer to a roadway than allowed by the Table
E-1 requirements should be classified as microscale or middle scale
rather than neighborhood or urban scale. If an open path analyzer is
used at a site, the monitoring path(s) must not cross over a roadway
with an average daily traffic count of 10,000 vehicles per day or
more. For those situations where a monitoring path crosses a roadway
with fewer than 10,000 vehicles per day, monitoring agencies must
consider the entire segment of the monitoring path in the area of
potential atmospheric interference form automobile emissions.
Therefore, this calculation must include the length of the
monitoring path over the roadway plus any segments of the monitoring
path that lie in the area between the roadway and minimum separation
distance, as determined form the Table E-1 of this appendix. The sum
of these distances must not be greater than 10 percent of the total
monitoring path length.
* * * * *
9. * * *
(c) No matter how nonreactive the sampling probe material is
initially, after a period of use reactive particulate matter is
deposited on the probe walls. Therefore, the time it takes the gas
to transfer from the probe inlet to the sampling device is also
critical. Ozone in the presence of nitrogen oxide (NO) will show
significant losses even in the most inert probe material when the
residence time exceeds 20 seconds.\26\ Other studies \27-28\
indicate that a 10 second or less residence time is easily
achievable. Therefore, sampling probes for reactive gas monitors at
NCore and at NO2 sites must have a sample residence time
less than 20 seconds.
* * * * *
11. Summary
Table E-4 of this appendix presents a summary of the general
requirements for probe and monitoring path siting criteria with
respect to distances and heights. It is apparent from Table E-4 that
different elevation distances above the ground are shown for the
various pollutants. The discussion in this appendix for each of the
pollutants describes reasons for elevating the monitor, probe, or
monitoring path. The differences in the specified range of heights
are based on the vertical concentration gradients. For CO and near-
road NO2 monitors, the gradients in the vertical
direction are very large for the microscale, so a small range of
heights are used. The upper limit of 15 meters is specified for the
consistency between pollutants and to allow the use of a single
manifold or monitoring path for monitoring more than one pollutant.
Table E-4 of Appendix E to Part 58. Summary of Probe and Monitoring Path Siting Criteria
--------------------------------------------------------------------------------------------------------------------------------------------------------
Horizontal and
vertical distance
Scale (maximum Height from ground to from supporting Distance from trees Distance from
Pollutant monitoring path probe, inlet or 80% of structures\2\ to to probe, inlet or roadways to probe,
length, meters) monitoring path \1\ probe, inlet or 90% 90% of monitoring inlet or monitoring
of monitoring path\1\ path\1\ (meters) path\1\ (meters)
(meters)
--------------------------------------------------------------------------------------------------------------------------------------------------------
SO2 3,4,5,6........................ Middle (300 m) 2-15.................. >1................... >10.................. N/A
Neighborhood Urban,
and Regional (1 km).
CO 4,5,7........................... Micro, middle (300 m), 3\1/2\: 2-15.......... >1................... >10.................. 2-10; see Table E-2
Neighborhood (1 km). of this appendix for
middle and
neighborhood scales.
O3 3,4,5........................... Middle (300 m) 2-15.................. >1................... >10.................. See Table E-1 of this
Neighborhood, Urban, appendix for all
and Regional (1 km). scales.
NO2 3,4,5.......................... Micro (Near-road [50- 2-7 (micro);.......... >1................... >10.................. <=50 meters for near-
300]). road microscale.
Middle (300m)......... 2-15 (all other ..................... .....................
scales).
Neighborhood, Urban, ...................... ..................... ..................... See Table E-1 of this
and Regional (1 km). appendix for all
other scales
Ozone precursors (for PAMS) 3 4 5.. Neighborhood and Urban 2-15.................. >1................... >10.................. See Table E-4 of this
(1 km). appendix for all
scales.
PM, Pb 3,4,5,6,8................... Micro: Middle, 2-7 (micro); 2-7 >2 (all scales, >10 (all scales)..... 2-10 (micro); see
Neighborhood, Urban (middle PM10 2.5); 2- horizontal distance Figure E-1 of this
and Regional. 15 (all other scales). only). appendix for all
other scales.
--------------------------------------------------------------------------------------------------------------------------------------------------------
N/A--Not applicable.
\1\ Monitoring path for open path analyzers is applicable only to middle or neighborhood scale CO monitoring, middle, neighborhood, urban, and regional
scale NO2 monitoring, and all applicable scales for monitoring SO2,O3, and O3 precursors.
\2\ When probe is located on a rooftop, this separation distance is in reference to walls, parapets, or penthouses located on roof.
\3\ Should be >20 meters from the dripline of tree(s) and must be 10 meters from the dripline when the tree(s) act as an obstruction.
\4\ Distance from sampler, probe, or 90% of monitoring path to obstacle, such as a building, must be at least twice the height the obstacle protrudes
above the sampler, probe, or monitoring path. Sites not meeting this criterion may be classified as middle scale (see text).
\5\ Must have unrestricted airflow 270 degrees around the probe or sampler; 180 degrees if the probe is on the side of a building or a wall.
[[Page 6537]]
\6\ The probe, sampler, or monitoring path should be away from minor sources, such as furnace or incineration flues. The separation distance is
dependent on the height of the minor source's emission point (such as a flue), the type of fuel or waste burned, and the quality of the fuel (sulfur,
ash, or lead content). This criterion is designed to avoid undue influences from minor sources.
\7\ For microscale CO monitoring sites, the probe must be >10 meters from a street intersection and preferably at a midblock location.
\8\ Collocated monitors must be within 4 meters of each other and at least 2 meters apart for flow rates greater than 200 liters/min or at least 1 meter
apart for samplers having flow rates less than 200 liters/min to preclude airflow interference.
* * * * *
14. Appendix G to Part 58 is amended as by revising paragraph 9 and
Table 2 to read as follows:
Appendix G to Part 58--Uniform Air Quality Index (AQI) and Daily
Reporting
* * * * *
9. How Does the AQI Relate to Air Pollution Levels?
For each pollutant, the AQI transforms ambient concentrations to
a scale from 0 to 500. The AQI is keyed as appropriate to the
national ambient air quality standards (NAAQS) for each pollutant.
In most cases, the index value of 100 is associated with the
numerical level of the short-term (i.e., averaging time of 24-hours
or less) standard for each pollutant. The index value of 50 is
associated with one of the following: the numerical level of the
annual standard for a pollutant, if there is one; one-half the level
of the short-term standard for the pollutant; or the level at which
it is appropriate to begin to provide guidance on cautionary
language. Higher categories of the index are based on increasingly
serious health effects that affect increasing proportions of the
population. An index value is calculated each day for each pollutant
(as described in section 12 of this appendix), unless that pollutant
is specifically excluded (see section 8 of this appendix). The
pollutant with the highest index value for the day is the
``critical'' pollutant, and must be included in the daily AQI
report. As a result, the AQI for any given day is equal to the index
value of the critical pollutant for that day. For the purposes of
reporting the AQI, the indexes for PM10 and
PM2.5 are to be considered separately.
* * * * *
Table 2--Breakpoints for the AQI
--------------------------------------------------------------------------------------------------------------------------------------------------------
These breakpoints Equal these AQIs
--------------------------------------------------------------------------------------------------------------------------------------------------------
PM2.5 PM10
O3 (ppm) 8- O3 (ppm) 1- ([micro]g/ ([micro]g/ CO (ppm) SO2 (ppm) NO2 (ppm) 1- AQI Category
hour hour\1\ m\3\) m\3\) hour
--------------------------------------------------------------------------------------------------------------------------------------------------------
0.000-0.059 ........... 0.0-15.4 0-54 0.0-4.4 0.000-0.034 0-0.053 0-50 Good.
0.060-0.075 ........... 15.5-40.4 55-154 4.5-9.4 0.035-0.144 0.054-0.100 51-100 Moderate.
0.076-0.095 0.125-0.164 40.5-65.4 155-254 9.5-12.4 0.145-0.224 0.101-0.360 101-150 Unhealthy for Sensitive Groups.
0.096-0.115 0.165-0.204 \3\ 65.5-150.4 255-354 12.5-15.4 0.225-0.304 0.361-0.64 151-200 Unhealthy.
0.116-0.374 0.205-0.404 \3\ 150.5- 355-424 15.5-30.4 0.305-0.604 0.65-1.24 201-300 Very Unhealthy.
250.4
(\2\) 0.405-0.504 \3\ 250.5- 425-504 30.5-40.4 0.605-0.804 1.25-1.64 301-400 Hazardous.
350.4
(\2\) 0.505-0.604 \3\ 350.5- 505-604 40.5-50.4 0.805-1.004 1.65-2.04 401-500 Hazardous.
500.4
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Areas are generally required to report the AQI based on 8-hour ozone values. However, there are a small number of areas where an AQI based on 1-hour
ozone values would be more precautionary. In these cases, in addition to calculating the 8-hour ozone index value, the 1-hour ozone index value may be
calculated, and the maximum of the two values reported.
\2\ 8-hours O3 values do not define higher AQI values (>=301). AQI values of 301 or greater are calculated with 1-hour O3 concentrations.
\3\ If a different SHL for PM2.5 is promulgated, these numbers will change accordingly.
[FR Doc. 2010-1990 Filed 2-8-10; 8:45 am]
BILLING CODE 6560-50-P