---
kind: "section"
citation: "40 C.F.R. § 51.907"
title: "40"
number: "51.907"
heading: "For an area that fails to attain the 8-hour NAAQS by its attainment date, how does EPA interpret sections 172(a)(2)(C)(ii) and 181(a)(5)(B) of the CAA?"
url: "https://uscodex.org/cfr/40/51.907"
---

# §51.907. For an area that fails to attain the 8-hour NAAQS by its attainment date, how does EPA interpret sections 172(a)(2)(C)(ii) and 181(a)(5)(B) of the CAA?


For purposes of applying sections [172(a)(2)(C)](/cfr/40/172.md?p=a-2-C) and [181(a)(5)](/cfr/40/181.md?p=a-5) of the CAA, an area will meet the requirement of section [172(a)(2)(C)(ii)](/cfr/40/172.md?p=a-2-C-ii) or [181(a)(5)(B)](/cfr/40/181.md?p=a-5-B) of the CAA pertaining to 1-year extensions of the attainment date if:

- (a) For the first 1-year extension, the area's 4th highest daily 8-hour average in the attainment year is 0.084 ppm or less.
- (b) For the second 1-year extension, the area's 4th highest daily 8-hour value, averaged over both the original attainment year and the first extension year, is 0.084 ppm or less.
- (c) For purposes of paragraphs [(a)](#a) and [(b)](#b) of this section, the area's 4th highest daily 8-hour average shall be from the monitor with the highest 4th highest daily 8-hour average of all the monitors that represent that area.

## Notes

### Source

Source: 69 FR 23996, Apr. 30, 2004, 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.