1. a) 1987 Primary and Secondary 24-Hour NAAQS for PM₁₀

   1. 1) The level of the 1987 primary and secondary 24-hour NAAQS for PM₁₀ is 150 μg/m³, 24-hour average concentration. The 1987 primary and secondary NAAQS for PM₁₀ is attained when the expected number of days per calendar year with a 24-hour average concentration above 150 μg/m³, as determined in accordance with appendix K to 40 CFR 50, incorporated by reference in Section 243.108, is equal to or less than one.
   2. 2) This subsection (a)(2) corresponds with 40 CFR 50.6(b), a provision marked "reserved" by USEPA. This statement maintains structural consistency with the corresponding federal regulation.

   3. 3) For the purpose of determining attainment of the 1987 primary and secondary 24-hour NAAQS for PM₁₀, particulate matter must be measured in the ambient air as PM₁₀ by a method that fulfills either of the following requirements:

      1. A) An FRM based on appendix J to 40 CFR 50, incorporated by reference in Section 243.108, and designated by USEPA and listed in List of Designated Methods, incorporated by reference in Section 243.108; or

      2. B) An FEM designated by USEPA and listed in List of Designated Methods, incorporated by reference in Section 243.108.

         BOARD NOTE: This subsection (a) is derived from 40 CFR 50.6.

2. b) 1997 Secondary Annual Average and Primary and Secondary 24-Hour NAAQS for PM_2.5

   1. 1) The 1997 secondary annual average NAAQS for PM_2.5 is 15.0 μg/m³, annual arithmetic mean concentration, and the 1997 primary and secondary 24-hour NAAQS for PM_2.5 is 65 μg/m³, 24-hour average concentration, measured in the ambient air as PM_2.5 by a method that fulfills either of the following requirements:

      1. A) An FRM based on appendix L of 40 CFR 50, incorporated by reference in Section 243.108, and designated by USEPA and listed in the List of Designated Methods, incorporated by reference in Section 243.108; or
      2. B) An FEM designated by USEPA and listed in the List of Designated Methods, incorporated by reference in Section 243.108.
   2. 2) The 1997 secondary annual average NAAQS for PM_2.5 is met when the annual arithmetic mean concentration, as determined in accordance with appendix N of 40 CFR 50, incorporated by reference in Section 243.108, is less than or equal to 15.0 μg/m³.

   3. 3) The 1997 primary and secondary 24-hour NAAQS for PM_2.5 is met when the 98^th percentile 24-hour concentration, as determined in accordance with appendix N of 40 CFR 50, incorporated by reference in Section 243.108, is less than or equal to 65 μg/m³.

      BOARD NOTE: This subsection (b) is derived from 40 CFR 50.7.

3. c) 2006 Secondary Annual Average and Primary and Secondary 24-Hour NAAQS for PM_2.5

   1. 1) The 2006 secondary annual average NAAQS for PM_2.5 is 15.0 μg/m³, annual arithmetic mean concentration, and the 2006 primary and secondary 24-hour NAAQS for PM_2.5 is 35 μg/m³, 24-hour average concentration, measured in the ambient air as PM_2.5 by a method that fulfills either of the following requirements:

      1. A) An FRM based on appendix L of 40 CFR 50, incorporated by reference in Section 243.108, and designated by USEPA and listed in the List of Designated Methods, incorporated by reference in Section 243.108; or
      2. B) An FEM designated by USEPA and listed in the List of Designated Methods, incorporated by reference in Section 243.108.
   2. 2) The 2006 secondary annual average NAAQS for PM_2.5 is met when the annual arithmetic mean concentration, as determined in accordance with appendix N of 40 CFR 50, incorporated by reference in Section 243.108, is less than or equal to 15.0 μg/m³.

   3. 3) The 2006 primary and secondary 24-hour NAAQS for PM_2.5 is met when the 98^th percentile 24-hour concentration, as determined in accordance with appendix N of 40 CFR 50, incorporated by reference in Section 243.108, is less than or equal to 35 μg/m³.

      BOARD NOTE: This subsection (c) is derived from 40 CFR 50.13.

4. d) 2012 Primary Annual Average and 24-Hour NAAQS for PM_2.5

   1. 1) The 2012 primary annual average NAAQS for PM_2.5 is 12.0 µg/m³ annual arithmetic mean concentration, and the 2012 primary 24-hour NAAQS for PM_2.5 is 35 µg/m³ 24-hour average concentration, measured in the ambient air as PM_2.5 by a method that fulfills either of the following requirements:

      1. A) An FRM based on appendix L of 40 CFR 50, incorporated by reference in Section 243.108, and designated by USEPA and listed in List of Designated Methods, incorporated by reference in Section 243.108; or
      2. B) An FEM designated by USEPA and listed in List of Designated Methods, incorporated by reference in Section 243.108.
   2. 2) The 2012 primary annual NAAQS for PM_2.5 is met when the annual arithmetic mean concentration, as determined in accordance with appendix N of 40 CFR 50, incorporated by reference in Section 243.108, is less than or equal to 12.0 µg/m³.

   3. 3) The 2012 primary 24-hour NAAQS for PM_2.5 is met when the 98^th percentile 24-hour concentration, as determined in accordance with appendix N of 40 CFR 50, incorporated by reference in Section 243.108, is less than or equal to 35 µg/m³.

      BOARD NOTE: This subsection (d) is derived from 40 CFR 50.18.

   4. e) 2024 Primary Annual Average and 24-Hour NAAQS for PM_2.5

      1. 1) The national primary ambient air quality standards for PM_2.5 are 9.0 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:

         1. A) An FRM based on appendix L of 40 CFR 50, incorporated by reference in Section 243.108, and designated by USEPA and listed in List of Designated Methods, incorporated by reference in Section 243.108; or
         2. B) An FEM designated by USEPA and listed in List of Designated Methods, incorporated by reference in Section 243.108.
      2. 2) The primary annual PM_2.5 standard is met when the annual arithmetic mean concentration, as determined in accordance with appendix N of 40 CFR 50, incorporated by reference in Section 243.108, is less than or equal to 9.0 µg/m³.

      3. 3) The primary 24-hour PM_2.5 standard is met when the 98^th percentile 24-hour concentration, as determined in accordance with appendix N of 40 CFR 50, incorporated by reference in Section 243.108, is less than or equal to 35 µg/m³.

         BOARD NOTE: This subsection (e) is derived from 40 CFR 50.20.

(Source: Amended at 48 Ill. Reg. 17597, effective November 21, 2024)