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(a) The national primary ambient air quality standards for PM2.5 are 12.0 micrograms per cubic meter (µg/m 3) annual arithmetic mean concentration and 35 µg/m 3 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 this part and designated in accordance with §53.11 of this chapter; or
(2) An equivalent method designated in accordance with §53.11 of this chapter.
(b) The primary annual PM2.5 standard is met when the annual arithmetic mean concentration, as determined in accordance with appendix N of this part, is less than or equal to 12.0 µg/m 3.
(c) The primary 24-hour PM2.5 standard is met when the 98th percentile 24-hour concentration, as determined in accordance with appendix N of this part, is less than or equal to 35 µg/m 3.
[78 FR 3277, Jan. 15, 2013]