---
kind: "section"
citation: "40 C.F.R. § 50.10"
title: "40"
number: "50.10"
heading: "National 8-hour primary and secondary ambient air quality standards for ozone."
url: "https://uscodex.org/cfr/40/50.10"
---

# §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](/cfr/40/part53.md) 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](/cfr/40/51.1100.md) 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](/cfr/40/50.15.md). 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](/cfr/40/51.1105.md), [§ 51.165](/cfr/40/51.165.md) and Appendix S to [part 51](/cfr/40/part51.md), the area designations and classifications with respect to the revoked 1997 ozone NAAQS are codified in [40 CFR part 81](/cfr/40/part81.md).

## Notes

### Amendments

[62 FR 38894, July 18, 1997, as amended at 77 FR 30170, May 21, 2012; 80 FR 12312, Mar. 6, 2015]

### Authority

Authority: 42 U.S.C. 7401, et seq.

### Source

Source: 36 FR 22384, Nov. 25, 1971, unless otherwise noted.

### Amendments

[62 FR 38894, July 18, 1997, as amended at 77 FR 30170, May 21, 2012; 80 FR 12312, Mar. 6, 2015]