National Ambient Air Quality Standard (NAAQS)


The Environmental Protection Agency (EPA) established the National Ambient Air Quality Standards (NAAQSs) as a measure to control national air pollution in 1970 as part of the Clean Air Act. The NAAQSs was amended to include controls for six of the most common air pollutants, sometimes referred to as criteria pollutants, first in 1971 to include carbon monoxide (C0), nitrogen oxides (NOX), ground-level ozone, particulate matter, and sulfur dioxide (SO2) and in 1977 lead (Pb) was added. Hydrocarbons originally appeared on the list of pollutants, but were removed in 1978 because they were considered by legislators to be adequately regulated through the ozone standard established in newer sections of the Clean Air Act. The provisions of the law allow the EPA to identify additional substances as pollutants and add them to the list as needed.


The NAAQSs were established based on the EPA's “criteria documents”, which summarize the effect on human health caused by each pollutant, based on current scientific knowledge. The standards are usually expressed in parts of pollutant per million parts of air (ppm) and vary in the duration of time a pollutant can be allowed into the environment, so that only a limited amount of contaminant may be emitted per hour, week, or year, for example. The 1977 Clean Air Act amendments require the EPA to submit criteria documents to the Clean Air Scientific Advisory Committee and the EPA's Science Advisory Board for review. Although standards should be based on scientific evidence, politics often become involved as environmentalists and public health advocates battle industrial powers in setting standards.

For each of the criteria pollutants primary and secondary standard may be set. The primary standards are designed to protect human health. Secondary standards are to protect crops, forests, and buildings if the primary standards are not capable of doing so; presently the only pollutant without a secondary standard is carbon monoxide. These standards apply uniformly throughout the country, in each of 247 air quality control regions. All parts of the country were required to meet the NAAQSs by 1975, but this deadline was extended, in some cases, to the year 2011. The states monitor air pollution, enforce the standards, and can implement stricter standards than the NAAQSs if they desire. These standards are typically acceptable emission levels during a time period, not to be exceeded more than a certain number of times for a designated period of time. For instance, carbon monoxide emissions cannot exceed 9 ppm in an 8 hour time frame more than once per year.


The six criteria pollutants come from a variety of sources and cause a host of health effects.


To achieve the NAAQSs for these six pollutants, the Clean Air Act incorporated three strategies. First, the federal government would establish new source performance standards (NSPSs) for stationary sources such as factories and power plants and emission standards for mobile sources. Finally, the states would develop state implementation plans (SIPs) to address existing sources of air pollution. If the federal government determined that a SIP was not adequate to assure that the state would meet the NAAQSs, it could impose federal controls to meet them. According to the EPA, the SIPs must be designed to bring substandard air quality regions up to the NAAQSs, or to make sure any area already meeting the requirements continued to do so. The SIPs are intended to prevent increased air pollution in areas of noncompliance, either by preventing significant expansions of existing industries or the opening of new plants. The EPA faced press to allow economic development and growth in such non-attainment areas while still working to reduce air pollution. The 1977 amendments to the Clean Air Act required that new sources of pollution in non-attainment areas control emissions to the lowest achievable emission rate (LAER) for that type of source and pollution and demonstrate that the new pollution would be offset by new emission reductions from existing sources in the area, reductions that went beyond existing permits and compliance plans. New sources were allowed, but only if the additional pollution was offset by reductions at existing sources.

See also Air pollution ; Clean Air Act (1963, 1970, 1977, 1990) ; Lead ; Ozone .



Schwartz, Joel. Air Quality in America: A Dose of Reality on Air Pollution Levels, Trends, and Health Risks. Washington, DC: AEI Press, 2008.


Environmental Protection Agency. “Air: Air Quality.” (accessed October 19, 2010).

Environmental Protection Agency. “Air: Air Quality: Monitoring.” (accessed October 19, 2010).

Environmental Protection Agency. “Air: Air Quality: Nonattainment.” (accessed October 1, 2012).

Environmental Protection Agency. “National Ambient Air Quality Standards (NAAQSs): Criteria.” (accessed October 1, 2012).


Environmental Protection Agency, 1200 Pennsylvania Ave. NW, Washington, DC, 20460, (202) 272-0167, .

Christopher McGrory Klyza
Alyson C. Heimer, MA

  This information is not a tool for self-diagnosis or a substitute for professional care.