Code of Federal Regulations Title 40. Protection of Environment § 40.50.7 National primary and secondary ambient air quality standards for PM 2.5

(a) The national primary and secondary ambient air quality standards for particulate matter are 15.0 micrograms per cubic meter (μg/m³) annual arithmetic mean concentration, and 65 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:

(b) The annual primary and secondary PM_2.5 standards are met when the annual arithmetic mean concentration, as determined in accordance with appendix N of this part, is less than or equal to 15.0 micrograms per cubic meter.

(c) The 24–hour primary and secondary PM_2.5 standards are met when the 98th percentile 24–hour concentration, as determined in accordance with appendix N of this part, is less than or equal to 65 micrograms per cubic meter.