Regulations last checked for updates: May 25, 2025

Title 40 - Protection of Environment last revised: Apr 25, 2028
Appendix - Table C-2 to Subpart C of Part 53—Sequence of Test Measurements
Measurement Concentration range
First set Second set
1LowMedium.
2HighHigh.
3MediumLow.
4HighHigh.
5LowMedium.
6MediumLow.
7LowMedium.
8MediumLow.
9HighHigh.
10MediumLow.
11HighMedium.
12LowHigh.
13MediumMedium.
14LowHigh.
15Low.
16Medium.
17Low.
18High.
authority: Sec. 301(a) of the Clean Air Act (42 U.S.C. sec. 1857g(a)), as amended by sec. 15(c)(2) of Pub. L. 91-604, 84 Stat. 1713, unless otherwise noted
source: 40 FR 7049, Feb. 18, 1975, unless otherwise noted.