15A NCAC 02D .0409 PM10 PARTICULATE MATTER (a) The ambient air quality standard for PM10 particulate matter is 150 micrograms per cubic meter (ug/m3), 24-hour average concentration. This standard is attained when 150 ug/m3, as determined according to Appendix N of 40 CFR Part 50, is not exceeded more than once per year on average over a three-year period. (b) For the purpose of determining attainment of the standards in Paragraph (a) of this Rule, particulate matter shall be measured in the ambient air as PM10 (particles with an aerodynamic diameter less than or equal to a nominal 10 micrometers) by either: (1) (2) History Note: a reference method based on Appendix M of 40 CFR Part 50 and designated according to 40 CFR Part 53; or an equivalent method designated according to 40 CFR Part 53. Authority G.S. 143-215.3(a)(1); 143-215.107(a)(3); Eff. July 1, 1988; Amended Eff. January 1, 2010; April 1, 1999.