15A NCAC 02D .0410 PM2.5 PARTICULATE MATTER (a) The ambient air quality standards for PM2.5 particulate matter are: (1) (2) 15.0 micrograms per cubic meter (ug/m3), annual arithmetic mean concentration; and 35 micrograms per cubic meter (ug/m3), 24-hour average concentration. These standards are attained when the annual arithmetic mean concentration is less than or equal to 15.0 ug/m3 and when the 98th percentile 24-hour concentration is less than or equal to 35 ug/m3, as determined according to Appendix N of 40 CFR Part 50. (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 PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) by either: (1) (2) History Note: a reference method based on Appendix L of 40 CFR Part 50 and designed according to 40 CFR Part 53; or an equivalent method designed according to 40 CFR Part 53. Authority G.S. 143-215.3(a)(1); 143-215.107(a)(3); Eff. April 1, 1999; Amended Eff. January 1, 2010.