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{{Short description|US EPA limits on certain air pollutants}}
[[File:NAAQS Non Attainment Counties 09302017.svg|thumb|350px|US counties that are designated "nonattainment" for the Clean Air Act's NAAQS, as of September 30, 2017
The U.S. '''National Ambient Air Quality Standards''' ('''NAAQS''', pronounced {{IPAc-en|ˈ|n|æ|k|s}} {{respell|naks}}) are limits on atmospheric concentration of six [[air pollution|pollutants]] that cause [[smog]], [[acid rain]], and other health hazards.<ref name=":1">{{Cite web|url=http://ohioepa.custhelp.com/app/answers/detail/a_id/907/~/definition-of-national-ambient-air-quality-standards-(naaqs)|title=Definition of National Ambient Air Quality Standards (NAAQS)|website=ohioepa.custhelp.com|language=en-US|access-date=2018-03-29}}</ref> Established by the [[United States Environmental Protection Agency]] (EPA) under authority of the [[Clean Air Act (United States)|Clean Air Act]] (42 U.S.C. 7401 et seq.), NAAQS is applied for outdoor air throughout the country.<ref name=":0">{{Cite web |url=http://tapseis.anl.gov/glossacro/dsp_wordpopup.cfm?word_id=444 |title=Trans-Alaska Pipeline System Renewal Environmental Impact Statement article |access-date=2009-10-12 |archive-url=https://web.archive.org/web/20171020191429/http://tapseis.anl.gov/glossacro/dsp_wordpopup.cfm?word_id=444 |archive-date=2017-10-20 |url-status=dead }}</ref>
The six '''criteria air pollutants''' (CAP), or '''criteria pollutants''', for which limits are set in the NAAQS are [[tropospheric ozone|ozone]] (O<sub>3</sub>), [[atmospheric particulate matter]] (PM<sub>2.5</sub>/PM<sub>10</sub>), [[lead]] (Pb), [[carbon monoxide]] (CO), [[sulfur oxide]]s (SO<sub>x</sub>), and [[nitrogen oxide]]s (NO<sub>x</sub>).<ref>{{Cite web|url=https://www.epa.gov/criteria-air-pollutants|title=Criteria Air Pollutants {{!}} US EPA|last=EPA, OAR|first=US|website=US EPA|date=9 April 2014|language=en|access-date=2018-01-18}}</ref> These are typically emitted from many sources in [[Industrial sector|industry]], [[mining]], [[transportation]], [[electricity generation]] and [[agriculture]]. In many cases they are the products of the [[combustion]] of [[fossil fuels]] or industrial processes.<ref>[http://des.nh.gov/organization/commissioner/pip/factsheets/ard/documents/ard-41.pdf Factsheet] des.nh.gov {{
The [[National Emissions Standards for Hazardous Air Pollutants]] cover many other chemicals, and require the maximum achievable reduction that the EPA determines is feasible.
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==Background==
The six criteria air pollutants were the first set of pollutants recognized by the [[United States]] [[Environmental Protection Agency]] as needing standards on a national level.<ref>Michigan Department Of Environmental Quality, January 2004. What is an Air Contaminant Pollutant? Fact Sheet</ref> The Clean Air Act requires the EPA to set US National Ambient Air Quality Standards (NAAQS) for the six CAPs.<ref>{{cite web |url=http://epa.gov/air/criteria.html |title=
The EPA established the NAAQS according to Sections 108 and 109 of the U.S. Clean Air Act, which was last amended in 1990.<ref>{{cite web |url=http://www.epa.gov/ttnnaaqs/ |url-status=dead |archive-url=https://web.archive.org/web/20090428102936/http://www.epa.gov/ttnnaaqs |archive-date=2009-04-28 |title=EPA - TTN NAAQS}}</ref> These sections require the EPA "(1) to list widespread air pollutants that reasonably may be expected to endanger public health or welfare; (2) to issue air quality criteria for them that assess the latest available scientific information on nature and effects of ambient exposure to them; (3) to set primary NAAQS to protect human health with adequate margin of safety and to set secondary NAAQS to protect against welfare effects (e.g., effects on vegetation, ecosystems, visibility, climate, manmade materials, etc); and (5) to periodically review and revise, as appropriate, the criteria and NAAQS for a given listed pollutant or class of pollutants."<ref name=":3">{{Cite web|url=http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=158823|title = Air Quality Criteria for Lead (Final Report, 2006)}}</ref>
==Descriptions==
# [[Ground level ozone]] (O<sub>3</sub>): Ozone found on the surface-level, also known as tropospheric ozone is also regulated by the NAAQS under the Clean Air Act. Ozone was originally found to be damaging to grapes in the 1950s. The US EPA set "oxidants" standards in 1971, which included ozone. These standards were created to reduce agricultural impacts and other related damages. Like lead, ozone requires a reexamination of new findings of health and vegetation effects periodically. This aspect necessitated the creation of a US EPA criteria document. Further analysis done in 1979 and 1997 made it necessary to significantly modify the pollution standards.
# [[Atmospheric particulate matter]]
#* PM<sub>10</sub>, coarse particles: 2.5 [[micrometre|micrometers]] (μm) to 10
#* PM<sub>2.5</sub>, fine particles: 2.5
# [[Lead]] (Pb): In the mid-1970s, lead was listed as a criteria air pollutant that required NAAQS regulation. In 1977, the EPA published a document which detailed the Air Quality Criteria for lead. This document was based on the scientific assessments of lead at the time. Based on this report (1977 Lead AQCD), the EPA established a "1.5
# [[Carbon monoxide]] (CO): The EPA set the first NAAQS for carbon monoxide in 1971. The primary standard was set at 9
# [[Sulfur oxide]]s (SO<sub>x</sub>): SO<sub>x</sub> refers to the oxides of sulfur, a highly reactive group of gases. SO<sub>2</sub> is of greatest interest and is used as the indicator for the entire SO<sub>x</sub> family. The EPA first set primary and secondary standards in 1971. Dual primary standards were set at 140
# [[Nitrogen oxide]]s (NO<sub>x</sub>): The EPA first set primary and secondary standards for the oxides of nitrogen in 1971. Among these are nitric oxide (NO), nitrous oxide (N<sub>2</sub>O), and nitrogen dioxide (NO<sub>2</sub>), all of which are covered in the NAAQS. NO<sub>2</sub> is the oxide measured and used as the indicator for the entire NO<sub>x</sub> family as it is of the most concern due to its quick formation and contribution to the formation of harmful ground level ozone.<ref name="airqualityNO">{{Cite web|url=http://www.epa.gov/airquality/nitrogenoxides/.|title = Air Quality Planning and Standards}}</ref> In 1971 the primary and secondary NAAQS for NO<sub>2</sub> were both set at an annual average of 0.053
::In April 2023, the EPA finalized its "Good Neighbor Plan", which phases in tighter standards for NO<sub>x</sub>, using a [[cap and trade]] system during the summer "ozone season". This is intended to reduce ground-level ozone in non-attainment areas downwind of industrial sources like power plants, incinerators, and industrial furnaces, often in other states.<ref>{{Cite web|url=https://www.epa.gov/newsreleases/epa-announces-final-good-neighbor-plan-cut-harmful-smog-protecting-health-millions|title=EPA Announces Final "Good Neighbor" Plan to Cut Harmful Smog, Protecting Health of Millions from Power Plant, Industrial Air Pollution|first=OA|last=US EPA|date=15 March 2023|website=www.epa.gov|accessdate=29 July 2023}}</ref>
==Standards==
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{| class="wikitable"
|-
! Pollutant !! Type !! Standard!! Averaging Time!!
|-
| rowspan="2" | [[Sulfur dioxide]] (SO<sub>2</sub>)
| Primary
| 75 ppb
| 1-hour
| 99th Percentile of 1-hour daily maximum concentrations, averaged over 3 years
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|-
| rowspan="3" | Fine particulate matter (PM<sub>2.5</sub>)
| Primary
| 9.0 μg/m<sup>3</sup> (12 μg/m<sup>3</sup> prior to May 6, 2024)<ref>{{cite web |url=https://www.federalregister.gov/documents/2024/03/06/2024-02637/reconsideration-of-the-national-ambient-air-quality-standards-for-particulate-matter |title=Reconsideration of the National Ambient Air Quality Standards for Particulate Matter |date=6 March 2024 |author=[[Environmental Protection Agency]]}}</ref>
| annual
| Annual mean, averaged over 3 years
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| Primary and Secondary
| 0.12 ppm (235 μg/m<sup>3</sup>)
| 1-hour{{ref|
| expected number of days per calendar year, with maximum hourly average concentration greater than 0.12
| {{USCFR|40|50|9|a}}
|-
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| {{USCFR|40|50|12|a}}
|}
* {{note|
* Source: [https://www.epa.gov/criteria-air-pollutants/naaqs-table USEPA]▼
▲*{{note|b|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: [https://www.epa.gov/criteria-air-pollutants/naaqs-table USEPA]
== Detection methods ==
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==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.<ref>{{
==See also==
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* [[Contamination control]]
* [[Clean Air Act (1990)]]
* [[Portable
* [[Toxic Substances Control Act of 1976]]
{{colend}}
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== External links ==
* [
* [
* [https://www.epa.gov/green-book EPA Green Book] showing non-attainment, maintenance, and attainment areas
* [
▲*[http://www.epaalumni.org/history/video/interview.cfm?id=38 EPA Alumni Association Oral History Video "Early Implementation of the Clean Air Act of 1970 in California.”]
{{Richard Nixon}}
{{US Environmental law}}
{{Natural resources}}
[[Category:Air pollution in the United States]]
[[Category:
[[Category:Environmental law in the United States]]
[[Category:Natural resource management]]▼
[[Category:Environmental science]]
[[Category:Environmental chemistry]]
▲[[Category:Natural resource management]]
[[Category:Smog]]
[[Category:United States Environmental Protection Agency]]
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