(a) The primary ambient air quality standards for PM2.5 shall be 9.0 micrograms per cubic meter (µg/m3) annual arithmetic mean concentration and 35 µg/m3 24-hour average concentration measured in the ambient air as PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) by either:
- (1) A reference method based on appendix L to 40 CFR Part 50 and designated in accordance with 40 CFR Part 53; or
- (2) An equivalent method designated in accordance with 40 CFR Part 53.
- (b) The primary annual PM2.5 standard shall be deemed met when the annual arithmetic mean concentration, as determined in accordance with Appendix N of 40 CFR Part 50, is less than or equal to 9.0 µg/m3.
- (c) The primary 24-hour PM2.5 standard shall be deemed met when the 98th percentile 24-hour concentration, as determined in accordance with Appendix N of 40 CFR Part 50, is less than or equal to 35 µg/m3.
History Note: Authority G.S. 143-215.3(a)(1); 143-215.107(a)(3);
Eff. April 1, 1999;
Amended Eff. September 1, 2015; January 1, 2010;
Readopted Eff. January 1, 2018;
Amended Eff. March 1, 2025.