National Ambient Air Quality Standards

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US counties that are designated "nonattainment" for the Clean Air Act's NAAQS. Valid 9/30/2017.

The U.S. National Ambient Air Quality Standards (NAAQS, pronounced \'naks\) are standards for harmful pollutants[1]. 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.[2]


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".[2]

EPA set NAAQS for six major pollutants listed as below. These six pollutants are also the criteria pollutants.[1]

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

Detection methods[edit]

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).[3] 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.[4] A complete list of FRMs and FEMs is available.[5]

Air quality control region[edit]

An air quality control region is an area, designated by the federal government, where communities share a common air pollution problem. [6]

See also[edit]


  1. ^ a b "Definition of National Ambient Air Quality Standards (NAAQS)". Retrieved 2018-03-29. 
  2. ^ a b Trans-Alaska Pipeline System Renewal Environmental Impact Statement article
  3. ^ 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 2017-06-27). ISSN 2166-465X. 
  4. ^ "EPA scientists develop Federal Reference & Equivalent Methods for measuring key air pollutants". U.S. Environmental Protection Agency. 2016-12-29. Retrieved 2017-06-28. 
  5. ^ 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. 
  6. ^ "EPA document". 

External links[edit]