Ambient Air Quality Standards

The National Ambient Air Quality Standards (NAAQS) are standards established by the United States Environmental Protection Agency

Pollutant	Type	Standard	Averaging Timea	Regulatory Citation
SO2	Primary	0.14 ppm (365 μg/m3)	24-hour	40 CFR 50.4(b)
SO2	Primary	0.030 ppm (80 μg/m³)	annual	40 CFR 50.4(a)
SO2	Secondary	0.5 ppm (1,300 μg/m³)	3-hour	40 CFR 50.5(a)
PM10	Primary and Secondary	150 μg/m³	24-hour	40 CFR 50.6(a)
PM2.5	Primary and Secondary	35 μg/m³	24-hour	40 CFR 50.7(a)
PM2.5	Primary and Secondary	15 μg/m³	annual	40 CFR 50.7(a)
CO	Primary	35 ppm (40 mg/m³)	1-hour	40 CFR 50.8(a)(2)
CO	Primary	9 ppm (10 mg/m³)	8-hour	40 CFR 50.8(a)(1)
O3	Primary and Secondary	0.12 ppm (235 μg/m³)	1-hourb	40 CFR 50.9(a)
O3	Primary and Secondary	0.075 ppm (150 μg/m³)	8-hour	40 CFR 50.10(a)
NO2	Primary and Secondary	0.053 ppm (100 μg/m³)	annual	40 CFR 50.11(a) and (b)
Pb	Primary and Secondary	0.15 μg/m³	Rolling 3 months	40 CFR 50.12

•  Each standard has its own criteria for how many times it may be exceeded, in some cases using a three year average.
• As of June 15, 2005, the 1-hour ozone standard no longer applies to areas designated with respect to the 8-hour ozone standard (which includes most of the United States, except for portions of 10 states).