[Code of Federal Regulations] [Title 40, Volume 2] [Revised as of July 1, 2003] From the U.S. Government Printing Office via GPO Access [CITE: 40CFR50.10] [Page 9] 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. 50.10 National 8-hour primary and secondary ambient air quality standards for ozone. (a) The level of the national 8-hour primary and secondary ambient air quality standards for ozone, measured by a reference method based on appendix D to this part and designated in accordance with part 53 of this chapter, is 0.08 parts per million (ppm), daily maximum 8-hour average. (b) The 8-hour primary and secondary ozone ambient air quality standards are met at an ambient air quality monitoring site when the average of the annual fourth-highest daily maximum 8-hour average ozone concentration is less than or equal to 0.08 ppm, as determined in accordance with appendix I to this part. [62 FR 38894, July 18, 1997]