C.F.R. » Title 40 » CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY › SUBCHAPTER C—AIR PROGRAMS › PART 50—NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDS

40 C.F.R. § 50.10

National 8-hour primary and secondary ambient air quality standards for ozone

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(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.

(c) Until the effective date of the final Implementation of the 2008 National Ambient Air Quality Standards for Ozone: State Implementation Plan Requirements Rule (final SIP Requirements Rule) to be codified at 40 CFR 51.1100 et seq., the 1997 ozone NAAQS set forth in this section will continue in effect, notwithstanding the promulgation of the 2008 ozone NAAQS under § 50.15. The 1997 ozone NAAQS set forth in this section will no longer apply upon the effective date of the final SIP Requirements Rule. For purposes of the anti-backsliding requirements of § 51.1105, § 51.165 and Appendix S to part 51, the area designations and classifications with respect to the revoked 1997 ozone NAAQS are codified in 40 CFR part 81.

[62 FR 38894, July 18, 1997, as amended at 77 FR 30170, May 21, 2012; 80 FR 12312, Mar. 6, 2015]
Notes of Decisions
Cited in 10 cases (1 in the last 5 years), 1975–2025 · leading case: Whitman v. American Trucking Assns., Inc.
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Whitman v. American Trucking Assns., Inc. (2001) scotus · cites it 2× “8202 (1979), would produce at best an inexact estimate of the new 8-hour averages, see 40 CFR § 50.10 , and App. I (1999). Also, to the extent that the new ozone standard is stricter than the old one, see Reply Brief for Petitioners in No.”
TOMAC v. Norton, Gale A. (2006) cadc “, in compliance with the CAA. While EPA had promulgated a more rigorous 8-hour standard in 1997 that put Berrien County’s attainment status in jeopardy, see National Ambient Air Quality Standards for Ozone, 62 Fed.”
Kentucky Resources Council, Inc. v. Environmental Protection Agency (2006) ca6 · cites it 2× “See 40 C.F.R. § 50.10 . The 8-hour standard applies throughout the nation, including the Northern Kentucky area.”
W.M. Barr & Co. v. South Coast Air Quality Management District (2012) calctapp “( 40 C.F.R. § 50.10 (2012).) In addition, the EPA has designated air quality control regions; metropolitan Los Angeles is one such area.”
Michigan v. U.S. Environmental Protection Agency (2000) cadc “38,856 (codified at 40 C.F.R. § 50.10 ). EPA has undertaken the phasing out of the 1-hour standard on an area-by-area basis, mandating that the standard would no longer apply to an area once it is “de-t.”
Louisiana Environmental Action Network v. United States Environmental Protection Agency (2004) ca5 “40 C.F.R. § 50.10 . However, the one-hour standard continues to apply to the Baton Rouge area.”
Movement Against Destruction v. Trainor (1975) mdd “40 C.F.R. § 50.10 , 36 F.R. 22384 (Nov. 25, 1971).”
PPG Industries, Inc. v. Costle (1981) cadc “40 C.F.R. § 50.10 . . The standard for emergency episodes is also based on a 24-hour period.”
Pennsylvania, Department of Environmental Protection v. Environmental Protection Agency (2005) cadc “40 C.F.R. § 50.10 . According to CAA procedures, once EPA promulgates a NAAQS, each State must submit proposed designations for all areas within its borders.”
Committee for a Better Arvin v. U.S. Environmental Protection Agency (2025) cand “08 parts per million 19 averaged over an 8-hour period, 40 C.F.R. § 50.10 ; 20 WHEREAS, EPA updated the ozone NAAQS in 2008 and revoked the 1997 ozone 21 NAAQ S, but is still required to determine whether an area attained the 1997 ozone NAAQS by 22 the area’s attainment date for…”
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