A. The national primary ambient air quality standards for PM_2.5 are 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 PM_2.5 (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 PM_2.5 standard is met when the annual arithmetic mean concentration, as determined in accordance with Appendix N to 40 CFR Part 50, is less than or equal to 9.0 µg/m³.

C. The primary 24-hour PM_2.5 standard is met when the 98th percentile 24-hour concentration, as determined in accordance with Appendix N to 40 CFR Part 50, is less than or equal to 35 µg/m³.