National Ambient Air Quality Standards, 2001-2016
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National Ambient Air Quality Standards (NAAQS) are federal air quality standards set by the Environmental Protection Agency (EPA) and implemented by state governments under the Clean Air Act. The standards are the maximum allowable levels for six pollutants. All states are required to have their own implementation plan to meet federal standards.[1]
Background
- See also: Clean Air Act
The Clean Air Act established nationwide air quality standards for six air pollutants known as criteria pollutants: ground-level ozone, sulfur dioxide, particulate matter, nitrogen oxide, carbon monoxide, and lead. These standards, known as National Ambient Air Quality Standards (NAAQS), set ceilings for the six air pollutants, and states enact state implementation plans outlining enforceable, source-specific emissions limits for these pollutants. Each state plan must show that the state will meet and maintain the NAAQS. In setting NAAQS, the EPA sets two standards for criteria pollutants—primary and secondary standards. Primary standards limit pollution to protect human health, and secondary standards limit pollution to protect against visibility impairment and damage to animals, vegetation, and buildings. If a geographical area exceeds the NAAQS for one or more of the six criteria pollutants, the area is considered by the EPA as a nonattainment area. Geographical areas with pollutant concentrations below the NAAQS are known as attainment areas.[2][3][4]
The Supreme Court upheld the legality of the NAAQS in Whitman v. American Trucking Associations (2001) and clarified the constitutional boundaries for the implementation of the standards.
The table below summarizes NAAQS standards, which are the maximum allowable amounts in a given period. Units of measure include parts per million (ppm) by volume, parts per billion (ppb) by volume, and micrograms per cubic meter of air (μg/m3).[5]
| National Ambient Air Quality Standards (as of March 22, 2016) | ||||
|---|---|---|---|---|
| Pollutant | Primary or secondary | Averaging time | Standard level | Form |
| Carbon monoxide | Primary | 8-hour | 9 ppm | Not to be exceeded more than once per year |
| Carbon monoxide | Primary | 1-hour | 35 ppm | Not to be exceeded more than once per year |
| Lead | Primary and secondary | Rolling 3-month average | 0.15 μg/m3 | Not to be exceeded |
| Nitrogen dioxide (NO2) | Primary | 1-hour | 100ppb | 98th percentile of 1-hour daily maximum, averaged over 3 years |
| Nitrogen dioxide | Primary and secondary | Annual | 53 ppb | Annual mean |
| Ozone (O3) | Primary and secondary | 8-hour | 0.070 ppm | Annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years |
| Particle pollution (PM2.5) | Primary | Annual | 12.0 μg/m3 | Annual mean, averaged over 3 years |
| Particle pollution (PM2.5) | Secondary | Annual | 15.0 μg/m3 | Annual mean, averaged over 3 years |
| Particle pollution (PM2.5) | Primary and secondary | 24 hours | 35.0 μg/m3 | 98th percentile, averaged over 3 years |
| Particle pollution (PM10) | Primary and secondary | 24 hours | 150.0 μg/m3 | Not to be exceeded more than once per year on average over 3 years |
| Sulfur dioxide (SO2) | Primary | 1-hour | 75 ppb | 99th percentile of 1-hour daily maximum concentrations, averaged over 3 years |
| Sulfur dioxide (SO2) | Secondary | 3-hour | 0.5 ppm | Not to be exceeded more than once per year |
| Source: U.S. Environmental Protection Agency, "NAAQS table," accessed May 10, 2016 | ||||
Current listings of nonattainment areas can be accessed here. The map below was prepared by the EPA and shows designated non-attainment areas in the United States as of April 22, 2016.[6][7]
State implementation plans
States must adopt a state implementation plan (SIP) designed to attain and maintain National Ambient Air Quality Standards (NAAQS). These plans are reviewed and approved by the EPA.[8]
State implementation plans must primarily include enforceable emissions limitations and other pollutant control measures to attain and maintain NAAQS for the six criteria pollutants. Other requirements for state plans include the following:[8]
- A schedule or timetable for compliance with NAAQS and other Clean Air Act requirements
- A permit program for sources of air pollution
- Plans for air quality monitoring in the state
- Prohibitions against emissions that may significantly contribute to another geographical area's inability to meet NAAQS
- Participation and consultations with local governments affected by a state plan
New Source Review Program
Under the Clean Air Act, the New Source Review Program (NSR) applies to major stationary sources of air pollution (sources with a potential to emit specified levels of a pollutant regulated under the act). Before a major stationary source is constructed or an existing source is significantly modified, the facility must undergo an NSR analysis. The NSR analysis requires a facility operator to review and analyze how the facility's emissions may impact air quality. Operators must show that the facility will not breach NAAQS or emissions limits found in the facility's permit, which must be obtained before the construction or modification of a facility begins. Permits, which are enforceable legal documents, include requirements for constructing and operating units that produce emissions at a facility and the technology required to limit emissions, among other requirements.[8]
See also
- Clean Air Act
- Whitman v. American Trucking Associations
- Glossary of environmental terms
- Air pollutants
- Hazardous air pollutant
Footnotes
- ↑ U.S. Environmental Protection Agency, "Glossary, N," accessed November 17, 2014
- ↑ U.S. Senate Environment and Public Works Committee, "Clean Air Act - Full Text," accessed June 11, 2017
- ↑ Environmental Protection Agency, "Applying or Implementing Ozone Standards," accessed June 1, 2017
- ↑ U.S. Environmental Protection Agency, "National Ambient Air Quality Standards (NAAQS)," accessed August 7, 2014
- ↑ U.S. Environmental Protection Agency, "National Ambient Air Quality Standards (NAAQS)," accessed August 7, 2014
- ↑ U.S. Environmental Protection Agency, "Current Nonattainment Counties for All Criteria Pollutants," updated July 2, 2014
- ↑ U.S. Environmental Protection Agency, "Counties Designated "Nonattainment" for Clean Air Act's National Ambient Air Quality Standards (NAAQS)," updated July 2, 2014
- ↑ 8.0 8.1 8.2 Congressional Research Service, "Clean Air Act: A Summary of the Act and Its Major Requirements," updated May 9, 2005
