RAPCA
The Regional Air Pollution Control Agency
Serving Clark, Darke, Greene, Miami, Montgomery and Preble Counties

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National Ambient Air Quality Standards

The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards (NAAQS) for wide-spread pollutants from numerous and diverse sources considered harmful to public health and the environment. The Clean Air Act established two types of national air quality standards. Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including protection against visibility impairment, damage to animals, crops, vegetation, and buildings. The Clean Air Act requires periodic review of the science upon which the standards are based and the standards themselves.

EPA has set NAAQS for six principal pollutants, which are called "criteria" pollutants:

*To learn more about each of these pollutants click on the link.

Below is a summary table of the current NAAQS:

Pollutant
Primary Stds.
Averaging Times
Secondary Stds.
Carbon Monoxide 9 ppm (10 mg/m3) 8-hour1 None
35 ppm
(40 mg/m3)
1-hour1 None
Lead 1.5 µg/m3 Quarterly Average Same as Primary
Nitrogen Dioxide 0.053 ppm
(100 µg/m3)
Annual (Arithmetic Mean) Same as Primary
Particulate Matter (PM10) 50 µg/m3
Annual2 (Arith. Mean)
Same as Primary
150 ug/m3 24-hour1  
Particulate Matter (PM2.5) 15 µg/m3
Annual3 (Arith. Mean)
Same as Primary
65 ug/m3 24-hour4  
Ozone 0.08 ppm 8-hour5 Same as Primary
0.12 ppm 1-hour6 Same as Primary
Sulfur Oxides 0.03 ppm Annual (Arith. Mean)
-------
0.14 ppm 24-hour1
-------
-------
3-hour1 0.5 ppm
(1300 ug/m3)

1 Not to be exceeded more than once per year.

2 To attain this standard, the expected annual arithmetic mean PM10 concentration at each monitor within an area must not exceed 50 ug/m3.

3 To attain this standard, the 3-year average of the annual arithmetic mean PM2.5 concentrations from single or multiple community-oriented monitors must not exceed 15 ug/m3.

4 To attain this standard, the 3-year average of the 98th percentile of 24-hour concentrations at each population-oriented monitor within an area must not exceed 65 ug/m3.

5 To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone concentrations measured at each monitor within an area over each year must not exceed 0.08 ppm.

6 (a) The standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm is <= 1, as determined by appendix H. (b) The 1-hour standard is applicable to all areas notwithstanding the promulgation of 8-hour ozone standards under Sec. 50.10. On June 2, 2003, (68 FR 32802) EPA proposed several options for when the 1-hour standard would no longer apply to an area.