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The National Ambient Air Quality Standards

Information on the standards established by the US Environmental Protection Agency on air quality.

The U.S. Environmental Protection Agency (EPA) has established National Ambient Air Quality Standards (NAAQS) for six air pollutants: ozone, lead, carbon monoxide, sulfur dioxide, nitrogen dioxide, and respirable particulate matter. The standards were established to protect the public from exposure to harmful amounts of pollutants. When the pollutant levels in an area have caused a violation of a particular standard, the area is classified as "nonattainment" for that pollutant. The EPA then imposes federal regulations on pollutant emissions and designates a time period in which the area must again attain the standard.

Air Pollution Concentrations Required
to Exceed the NAAQS
Pollutant Averaging Period Standard Primary NAAQS Secondary NAAQS

Ozone

8- Hour

The average of the annual fourth highest daily eight-hour maximum over a three-year period is not to be at or above this level.

76 ppb 76 ppb

Carbon Monoxide

1- Hour

Not to be at or above this level more than once per calendar year.

35.5 ppm -

8- Hour

Not to be at or above this level more than once per calendar year.

9.5 ppm -

Sulfur Dioxide

1- Hour

Three year average of the annual 99th percentile of the daily maximum 1-hour averages not to be at or above this level.

76 ppb -
3 - Hour

Not to be at or above this level more than once per calendar year.

- 550 ppb

Nitrogen Dioxide

1 - Hour

Three year average of the annual 98th percentile of the daily maximum 1-hour averages not to be at or above this level.

101 ppb -
Annual

Not to be at or above this level.

54 ppb 54 ppb

Respirable Particulate Matter (10 microns or less) (PM10)

24 - Hour

Not to be at or above this level on more than three days over three years with daily sampling.

155 µg/m3 155 µg/m3
Annual

The three-year average of annual arithmetic mean concentrations at each monitor within an area is not to be at or above this level.

51 µg/m3 51 µg/m3

Respirable Particulate Matter (2.5 microns or less) (PM2.5)

24 - Hour

The three-year average of the annual 98th percentile for each population-oriented monitor within an area is not to be at or above this level.

36 µg/m3 36 µg/m3
Annual

The three-year average of annual arithmetic mean concentrations from single or multiple community-oriented monitors is not to be at or above this level.

15.1 µg/m3 15.1 µg/m3

Lead

3 - Month

Three-month rolling average not to be at or above this level.

0.16 µg/m3 0.16 µg/m3
Quarter

Not to be at or above this level.

1.55 µg/m3 1.55 µg/m3

 

Primary NAAQS: the levels of air quality that the EPA judges necessary, with an adequate margin of safety, to protect the public health.

 

Secondary NAAQS: the levels of air quality that the EPA judges necessary to protect the public welfare from any known or anticipated adverse effects.

 

EPA - National Ambient Air Quality Standards (NAAQS) Exit TCEQ

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