(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 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:

(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 µg/m³.

(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 35 µg/m³.

(d) Until the effective date of the final Fine Particulate Matter National Ambient Air Quality Standards: State Implementation Plan Requirements rule to be codified at 40 CFR 51.1000 through 51.1016, the 1997 annual PM_2.5 NAAQS set forth in this section will continue in effect, notwithstanding the promulgation of the 2012 primary annual PM_2.5 NAAQS under § 50.18. The 1997 primary annual PM_2.5 NAAQS set forth in this section will no longer apply upon the effective date of the final Fine Particulate Matter National Ambient Air Quality Standards: State Implementation Plan Requirements rule; except that for areas designated nonattainment for the 1997 annual PM_2.5 NAAQS set forth in this section as of the effective date of the final Fine Particulate Matter National Ambient Air Quality Standards: State Implementation Plan Requirements rule, the requirements applicable to the 1997 primary annual PM_2.5 NAAQS set forth in this section will apply until the effective date of an area's redesignation to attainment for the 1997 annual PM_2.5 NAAQS pursuant to the requirements of section 107 of the Clean Air Act. The 1997 secondary annual PM_2.5 NAAQS and the 1997 24-hour PM_2.5 NAAQS shall remain in effect. The area designations and classifications with respect to the 1997 annual and 24-hour PM_2.5 NAAQS remain codified in 40 CFR part 81 in order to provide information on where the 1997 primary annual PM_2.5 NAAQS has been revoked and to facilitate the implementation of the 1997 secondary annual PM_2.5 NAAQS and the 1997 24-hour PM_2.5 NAAQS.