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 , 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".
Standards are required to "accurately reflect the latest scientific knowledge," and are reviewed every five years by a Clean Air Scientific Advisory Committee (CASAC), consisting of "seven members appointed by the EPA administrator."
The CASAC subcommittees which provide scientific input on particulate matter and ozone were terminated in October 2018."
The EPA declined to state why the Particulate Matter Review Panel, which "is responsible for helping the agency decide what levels of pollutants are safe to breathe," will not be reconvened in 2019.
Former CASAC chair Bernard D. Goldstein, M.D., who served as EPA Assistant Administrator for R&D under President Reagan, described the decision as "the latest saga of EPA’s divorce proceedings against environmental science."
EPA has 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|
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 regionEdit
An air quality control region is an area, designated by the federal government, where communities share a common air pollution problem. 
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