---
kind: "section"
citation: "40 C.F.R. § 51.1107"
title: "40"
number: "51.1107"
heading: "Determining eligibility for 1-year attainment date extensions for the 2008 ozone NAAQS under CAA section 181(a)(5)."
url: "https://uscodex.org/cfr/40/51.1107"
---

# §51.1107. Determining eligibility for 1-year attainment date extensions for the 2008 ozone NAAQS under CAA section 181(a)(5).

- (a) A nonattainment area will meet the requirement of CAA [section 181(a)(5)(B)](/cfr/40/181.md?p=a-5-B) pertaining to 1-year extensions of the attainment date if:
  - (1) For the first 1-year extension, the area's 4th highest daily maximum 8 hour average in the attainment year is 0.075 ppm or less.
  - (2) For the second 1-year extension, the area's 4th highest daily maximum 8 hour value, averaged over both the original attainment year and the first extension year, is 0.075 ppm or less.
- (b) For purposes of [paragraph (a)](#a) of this section, the area's 4th highest daily maximum 8 hour average for a year shall be from the monitor with the highest 4th highest daily maximum 8 hour average for that year of all the monitors that represent that area.

## Notes

### Amendments

[80 FR 12314, Mar. 6, 2015]

### Source

Source: 77 FR 30170, May 21, 2012, unless otherwise noted.

### Authority

Authority: 23 U.S.C. 101; 42 U.S.C. 7401-7671q.

### Source

Source: 36 FR 22398, Nov. 25, 1971, unless otherwise noted.

### Amendments

[80 FR 12314, Mar. 6, 2015]