Regulations last checked for updates: Jan 18, 2025

Title 40 - Protection of Environment last revised: Dec 30, 2025
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.