National Ambient Air Quality Standards
The U.S. National Ambient Air Quality Standards (NAAQS, pronounced \'naks\) are standards for harmful pollutants. Established by the United States Environmental Protection Agency (EPA) under authority of the Clean Air Act (42 U.S.C. 7401 et seq.), NAAQS is applied for outdoor air throughout the country.
The standards are listed in 40 C.F.R. 50. Primary standards are designed to protect human health, with an adequate margin of safety, including sensitive populations such as children, the elderly, and individuals suffering from respiratory diseases. Secondary standards are designed to protect public welfare (including effects on soils, water, crops, vegetation, man-made materials, animals, wildlife, weather, visibility, and climate), damage to property, transportation hazards, economic values, and personal comfort and well-being from any known or anticipated adverse effects of a pollutant. A district meeting a given standard is known as an "attainment area" for that standard, and otherwise a "non-attainment area".
EPA set NAAQS for six major pollutants listed as below. These six pollutants are also the criteria pollutants.
|Pollutant||Type||Standard||Averaging Time||Forma||Regulatory Citation|
|Sulfur dioxide (SO2)||Primary||75 ppb||1-hour||99th Percentile of 1-hour daily maximum concentrations, averaged over 3 years||40 C.F.R. 50.17a|
|Secondary||0.5 ppm (1,300 μg/m³)||3-hour||Not to be exceeded more than once per year||40 C.F.R. 50.5a|
|Particulate matter (PM10)||Primary and Secondary||150 μg/m³||24-hour||Not to be exceeded more than once per year on average over 3 years||40 C.F.R. 50.6a|
|Fine particulate matter (PM2.5)||Primary||12 μg/m³||annual||Annual mean, averaged over 3 years||40 C.F.R. 50.18a|
|Secondary||15 μg/m³||annual||Annual mean, averaged over 3 years||40 C.F.R. 50.7a|
|Primary and Secondary||35 μg/m³||24-hour||98th percentile, averaged over 3 years||40 C.F.R. 50.18a|
|Carbon monoxide (CO)||Primary||35 ppm (40 mg/m³)||1-hour||Not to be exceeded more than once per year||40 C.F.R. 50.8a(2)|
|Primary||9 ppm (10 mg/m³)||8-hour||Not to be exceeded more than once per year||40 C.F.R. 50.8a(1)|
|Ozone (O3)||Primary and Secondary||0.12 ppm (235 μg/m³)||1-hourb||expected number of days per calendar year, with maximum hourly average concentration greater than 0.12 ppm, is equal to or less than 1||40 C.F.R. 50.9a|
|Primary and Secondary||0.070 ppm (140 μg/m³)||8-hour||Annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years||40 C.F.R. 50.19a|
|Nitrogen dioxide (NO2)||Primary and Secondary||0.053 ppm (100 μg/m³)||annual||Annual mean||40 C.F.R. 50.11ab|
|Lead (Pb)||Primary and Secondary||0.15 μg/m³||Rolling 3 months||Not to be exceeded||40 C.F.R. 50.12a|
- ^a Each standard has its own criteria for how many times it may be exceeded
- ^b 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).
- Source: USEPA
The EPA National Exposure Research Laboratory can designate a measurement device using an established technological basis as a Federal Reference Method (FRM) to certify that the device has undergone a testing and analysis protocol, and can be used to monitor NAAQS compliance. Devices based on new technologies can be designated as a Federal Equivalent Method (FEM). FEMs are based on different sampling and/or analyzing technologies than FRMs, but are required to provide the same decision making quality when making NAAQS attainment determinations. Approved new methods are formally announced through publication in the Federal Register. A complete list of FRMs and FEMs is available.
Air quality control region
An air quality control region is an area, designated by the federal government, where communities share a common air pollution problem. 
- Air pollution
- Air Quality Index
- Atmospheric dispersion modeling
- Clean Air Act (1990)
- Portable Emissions Measurement System
- Toxic Substances Control Act of 1976
- "Definition of National Ambient Air Quality Standards (NAAQS)". ohioepa.custhelp.com. Retrieved 2018-03-29.
- Trans-Alaska Pipeline System Renewal Environmental Impact Statement article
- “Early Implementation of the Clean Air Act of 1970 in California.” EPA Alumni Association. Video, Transcript (see p4). July 12, 2016.
- Hall, Eric S.; Kaushik, Surender M.; Vanderpool, Robert W.; Duvall, Rachelle M.; Beaver, Melinda R.; Long, Russell W.; Solomon, Paul A.; Hall, Eric S.; Kaushik, Surender M. (2014). "Integrating Sensor Monitoring Technology into the Current Air Pollution Regulatory Support Paradigm: Practical Considerations". American Journal of Environmental Engineering. 4 (6). doi:10.5923/j.ajee.20140406.02 (inactive 2018-09-22). ISSN 2166-465X.
- "EPA scientists develop Federal Reference & Equivalent Methods for measuring key air pollutants". U.S. Environmental Protection Agency. 2016-12-29. Retrieved 2017-06-28.
- Gilliam, Joseph H.; Hall, Eric S. (2016-07-13). "Reference and Equivalent Methods Used to Measure National Ambient Air Quality Standards (NAAQS) Criteria Air Pollutants - Volume I". U.S. Environmental Protection Agency. Retrieved 2017-06-28.
- "EPA document".
- EPA summary of the National Ambient Air Quality Standards
- EPA summary for Air & Radiation
- EPA Green Book showing non-attainment, maintenance, and attainment areas
- Most Polluted Cities, 2005 – American Lung Association
- EPA Alumni Association Oral History Video "Early Implementation of the Clean Air Act of 1970 in California.”