[Code of Federal Regulations]
[Title 40, Volume 2]
[Revised as of July 1, 2009]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR50.1]

[Page 5-6]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 50_NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY 
STANDARDS--Table of Contents
 
Sec. 50.1  Definitions.

    (a) As used in this part, all terms not defined herein shall have 
the meaning given them by the Act.
    (b) Act means the Clean Air Act, as amended (42 U.S.C. 1857-18571, 
as amended by Pub. L. 91-604).
    (c) Agency means the Environmental Protection Agency.
    (d) Administrator means the Administrator of the Environmental 
Protection Agency.
    (e) Ambient air means that portion of the atmosphere, external to 
buildings, to which the general public has access.

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    (f) Reference method means a method of sampling and analyzing the 
ambient air for an air pollutant that is specified as a reference method 
in an appendix to this part, or a method that has been designated as a 
reference method in accordance with part 53 of this chapter; it does not 
include a method for which a reference method designation has been 
cancelled in accordance with Sec. 53.11 or Sec. 53.16 of this chapter.
    (g) Equivalent method means a method of sampling and analyzing the 
ambient air for an air pollutant that has been designated as an 
equivalent method in accordance with part 53 of this chapter; it does 
not include a method for which an equivalent method designation has been 
cancelled in accordance with Sec. 53.11 or Sec. 53.16 of this chapter.
    (h) Traceable means that a local standard has been compared and 
certified either directly or via not more than one intermediate 
standard, to a primary standard such as a National Bureau of Standards 
Standard Reference Material (NBS SRM), or a USEPA/NBS-approved Certified 
Reference Material (CRM).
    (i) Indian country is as defined in 18 U.S.C. 1151.
    (j) Exceptional event means an event that affects air quality, is 
not reasonably controllable or preventable, is an event caused by human 
activity that is unlikely to recur at a particular location or a natural 
event, and is determined by the Administrator in accordance with 40 CFR 
50.14 to be an exceptional event. It does not include stagnation of air 
masses or meteorological inversions, a meteorological event involving 
high temperatures or lack of precipitation, or air pollution relating to 
source noncompliance.
    (k) Natural event means an event in which human activity plays 
little or no direct causal role.
    (l) Exceedance with respect to a national ambient air quality 
standard means one occurrence of a measured or modeled concentration 
that exceeds the specified concentration level of such standard for the 
averaging period specified by the standard.

[36 FR 22384, Nov. 25, 1971, as amended at 41 FR 11253, Mar. 17, 1976; 
48 FR 2529, Jan. 20, 1983; 63 FR 7274, Feb. 12, 1998; 72 FR 13580, Mar. 
22, 2007]