National Ambient Air Quality Standards (NAAQS)

Averaging Period Primary
Standard
Secondary
Standard
Notes
Carbon Monoxide
8-hour average 9 ppm 9 ppm (1)
1-hour average 35 ppm 35 ppm (1)
Lead
3-month rolling average 0.15 µg/m3 0.15 µg/m3 (2)
Quarterly average 1.5 µg/m3 1.5 µg/m3
Nitrogen Dioxide
1-hour average 0.100 ppm (3)
Annual average 0.053 ppm 0.053 ppm
Ozone
1-hour average 0.12 ppm 0.12 ppm (4)
8-hour average 0.075 ppm 0.075 ppm (5)
PM10 (Inhalable Particulates)
Annual average 50 µg/m3 50 µg/m3 (6)
24-hour average 150 µg/m3 150 µg/m3 (7)
PM2.5 (Fine Particulates)
Annual average 15 µg/m3 15 µg/m3 (6)
24 hour average 35 µg/m3 35 µg/m3 (8)
Sulfur Dioxide
Annual average 0.03 ppm  
24-hour average 0.14 ppm (1)
3-hour average 0.50 ppm (1)

FOOTNOTES:

(1) This average is not to be exceeded more than once per year.

(2) The lead standard was revised 10/15/2008.

(3) The standard is attained when the 3-year average of the 98th percentile of the annual distribution of daily maximum 1-hour average concentrations is less than the standard.  The NO2 standard was revised 1/22/2010.

(4) The standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above the standard is equal to or less than 1 over a three-year period, as determined by Appendix H of 40 CFR 50.

(5) The standard is attained when the three-year average of the fourth-highest daily maximum 8-hour average is less than or equal to the standard.  The ozone standard was revised 3/27/2008.

(6) The standard is attained when the expected annual arithmetic mean concentration, as determined in accordance with Appendix K to 40 CFR 50, is less than or equal to the standard.

(7) The standard is attained when the 3-year average of the annual 99th percentile concentration is less than the standard.

(8) The standard is attained when the 98th percentile concentration for the year is less than the standard.  The PM2.5 standard was revised 10/17/2006.