Code of Federal Regulations Title 40. Protection of Environment § 40.51.907 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?

(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) and (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.