StacksVerified U.S. regulatory reference

40 CFR §51.907

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
For purposes of applying sections 172(a)(2)(C) and 181(a)(5) of the CAA, an area will meet the requirement of section 172(a)(2)(C)(ii) or 181(a)(5)(B) of the CAA pertaining to 1-year extensions of the attainment date if:
  1. (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.
  2. (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.
  3. (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.