National Air Quality StandardsA

Pollutant Averaging Time Primary StandardsB Secondary StandardsC
SO2 Annual Arithmetic Mean 80 µg/m3 (0.03 ppm)
24 hours 365 µg/m3 (0.14 ppm)
3 hours 1300 µg/m3 (0.5 ppm)
PM10D Annual Arithmetic Mean 50 µg/m3 Same as Primary Standard
24 hours 150 µg/m3 Same as Primary Standard
CO 8 hours 9 ppm Same as Primary Standard
1 hour 35 ppm Same as Primary Standard
O3E 1 hour 0.125 ppm Same as Primary Standard
8 hour 0.08 ppm Same as Primary Standard
NO2 Annual Arithmetic Mean (0.05 ppm) 100 µg/m3 Same as Primary Standard
Pb Calendar Quarter Arithmetic Mean 1.5 µg/m3 Same as Primary Standard
A
National standards, other than those based on annual arithmetic means, are not to be exceeded more than once a year.
B
National Primary Standards: The levels of air quality necessary, with an adequate margin of safety, to protect the public health.
C
National Secondary Standards: The levels of air quality necessary to protect the public welfare from any known or anticipated adverse effects of a pollutant.
D
PM10 replaced TSP as the ambient particulate standard effective July 31, 1987, and includes only those particles with an aerodynamic diameter of less than or equal to a nominal 10 microns. Expected number of exceedances shall not be more than one per year (3 year average) as determined by Appendix K of 40CFR Part 50.
E
1-Hour
Expected number of exceedance days shall not be more than one per year (3 year average) as determined by Appendix K of 40CFR Part 50.
8-Hour
The standards are met at an ambient air quality site when the 3-year average of the annual fourth-highest daily maximum 8-hour average ozone concentration is less than or equal to 0.08 ppm.
Both standards (1 and 8 hour) apply until the first standard (1 hour) is met, after which, only the 8 hour standard will apply.
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Steven McDougall / swmcd@theworld.com / 1998 December 03