NATIONAL AMBIENT AIR QUALITY STANDARDS (NAAQS)

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This includes the new standards promulgated in July, 1997.

NAAQS establishes concentration limits for criteria pollutants, i.e. those pollutants with a well-established dose/response relationship. Acute refers to concentrations that may lead to immediate death or illness, and chronic refers to concetrations where the health effects may materialize in the longer term. Primary standards are those that are deemed minimal to preserve human life, and secondary standards are those that are deemed minimal to preserve the environment as a whole.

Pollutant	Averaging Time	Primary Standard	Secondary Standard
Particulate Matter -- Diameter .lt. 10 micrometers (PM-10)	Annual arithmetic mean.	Chronic: 50 micrograms/m3.	Same.
	24-hour arithmetic mean, 99th percentile, average over 3 years.	Acute: 150 micrograms/m3.
Particulate Matter -- Diameter .lt. 2.5 micrometers (PM-2.5).	Annual arithmetic mean.	Chronic: 15 micrograms/m3.	Same.
	24-hour arithmetic mean, 98th percentile, average over 3 years.	Acute: 65 micrograms/m3.
Ozone (O3)	8-hour, 3-year average of the annual 4th highest daily maximum 8-hour concentration.	0.08 parts per million (ppm).	Same.
Sulfur Dioxide (SO2)	Annual arithmetic mean.	Chronic: 80 micrograms/m3.
	24-hour, not to be exceeded more than once per year.	Acute: 365 micrograms/m3.
	3-hour, not to be exceeded more than once per year.		Acute: 1300 micrograms/m3
Nitrogen Dioxide (NO2).	Annual arithmetic mean.	1300 micrograms/m3.	Same.
Carbon Monoxide (CO)	8-hour, not to be exceeded more than once per year.	Chronic: 10 milligrams/m3 (10,000 micrograms/m3).
	1-hour, not to be exceeded more than once per year.	Acute: 40 milligrams/m3 (40,000 micrograms/m3).

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This page was last updated on 10/04/2002.