Air Quality
| National Ambient Air Quality Standards (NAAQS) |
The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) for pollutants considered harmful to public health and the environment. The Clean Air Act established two types of national air quality standards. Primary standards are set to protect public health, and secondary standards are set to protect public welfare. A complete description of nonattainment areas can found at 40 CFR 50 – National Primary and Secondary Ambient Air Quality Standards.
The EPA Office of Air Quality Planning and Standards has set NAAQS for six principal pollutants, which are called "criteria" pollutants. Units of measure for the standards may be reported in parts per million (ppm), milligrams per cubic meter of air (mg/m3), and micrograms per cubic meter of air (µg/m3).
Areas which consistently violate the NAAQS because of man-caused activities are classified as "nonattainment" areas, and must implement a plan to reduce ambient concentrations below the maximum pollution standards. There are approximately 370 "nonattainment" areas for different pollutants in the country, located mostly in urban areas, locations downwind of large industrial regions, or in areas with limited dispersion conditions.
Areas which once violated the NAAQS (previous nonattainment areas), but now achieve the standards as a result of intensive management practices (e.g.; oxygenated fuels, "lowest achievable emission rate" control technology, etc.) are classified as "maintenance" areas, and must implement a plan to maintain ambient concentrations below the maximum pollution standards. There are approximately 300 "maintenance" areas for different pollutants in the country.
Areas which demonstrate they achieve the NAAQS through air pollutant monitoring are classified "attainment," whereas those areas which do not have monitoring data, but are assumed to achieve the NAAQS due to a generally low number and size of emission sources are "unclassified" (neither "attainment" nor "nonattainment"). Most rural areas of the country have been designated as either "attainment" or "unclassified" for all pollutants. Under EPA's "Fugitive Dust Policy," areas which violate the particulate matter standards, but lack significant industrial or population particulate sources to cause such violations are also "unclassified."
The American Trucking Association challenged whether the Clean Air Act requires that EPA must ignore all factors other than health effects when setting primary national air quality standards. Oral arguments were heard by the U.S. Supreme Court on November 7, 2000, as reported by the Environment News Service (pdf). On February 27, 2001, the Court issued it's findings (also reported by the Environment News Service (pdf)), stating that the Clean Air Act "unambiguously bars cost considerations" when EPA sets air quality standards, but that EPA can consider costs when directing the State's on how to implement the new standards. The Court further directed EPA to revise it's previously proposed methods to implement the new 8-hour ozone and fine particulate matter (PM-2.5) ambient air quality standards.
| Pollutant | Averaging Time (a/) | Primary Standard (b/) | Secondary Standard (c/) |
| Carbon monoxide | 8-hour | 10,000 | 10,000 |
| 1-hour | 40,000 | 40,000 | |
| Lead | Quarterly | 1.5 | 1.5 |
| Nitrogen dioxide | Annual | 100 | 100 |
| Ozone | 8-hour | 157 | 157 |
| 1-hour (d/) | 235 | 235 | |
| Sulfur dioxide | Annual | 80 | ---- |
| 24-hour | 365 | ---- | |
| 3-hour | ---- | 1,300 | |
| Particulate Matter (PM-10) | Annual | 50 | 50 |
| 24-hour | 150 | 150 | |
| Particulate Matter (PM-2.5) | Annual | 15 | 15 |
| 24-hour | 65 | 65 |
Sources: 40 CFR 50.4 through 50.12; 40 CFR 51.166(c) and 52.21(c); 62 FR 38652 and 62 FR 38856 (July 1, 2000)
(a/) Annual standards are not to be exceeded; short-term standards may be exceeded once per year.
(b/) Primary standards are designed to protect public health.
(c/) Secondary standards are designed to protect public welfare.
(d/) The1-hour ozone standards are to be implemented on an interim basis until the 8-hour standards go into full effect.
| Designated Nonattainment Areas |
The Clean Air Act defines a "nonattainment area" as a locality where air pollution levels persistently exceed National Ambient Air Quality Standards. Designating an area nonattainment is a formal rulemaking process and EPA normally takes this action only after the air quality standards have been exceeded for several consecutive years. A complete description of nonattainment areas can found at 40 CFR 81– Designation of Areas for Air Quality Planning Purposes. A simplified listing of nonattainment areas derived from 40 CFR 81, as published in the Federal Register, is also available (pdf). Areas are listed in alphabetical order by state.
Pollutants are: CO = carbon monoxide, lead, NO2 = nitrogen dioxide, ozone (1-hr), SO2 = sulfur dioxide and PM-10 = particulate matter smaller than 10 micrometers in effective diameter. For more information on these areas see the EPA Green Book.
Detailed maps showing nonattainment areas by county (entire county as red, partial county as yellow) are available for all pollutants combined and the following individual criteria pollutants:
Carbon monoxide
Lead
Nitrogen dioxide - There are curently no nitrogen dioxide nonattainment areas.
Ozone (1-hour)
Particulate matter (PM-10)
Sulfur dioxide
Although the recent U.S. Supreme Court decision supported EPA's proposed new 8-hour ozone and fine particulate matter (PM-2.5) ambient air quality standards, it will be sometime before the new standards will go into effect. Eventually, EPA will formally designate new nonattainment areas. Until then, here are some potential additional nonattainment area designations:
| Designated Maintenance Areas |
The Clean Air Act defines a "maintenance area" as the geographic region previously designated nonattainment, and subsequently redesignated to attainment. Designating an area as "maintenance" is a formal rulemaking process and EPA takes this action only after monitoring data demonstrate the air quality standards are being met, and a maintenance plan has been developed under section 175A of the Clean Air Act. A simplified listing of maintenance areas derived from Title 40, Code of Federal Regulations, part 81 (40 CFR 81), as published in the Federal Register, is also available (pdf). Areas are listed in alphabetical order by state.
Pollutants are: CO = carbon monoxide, lead, NO2 = nitrogen dioxide, ozone (1-hr), SO2 = sulfur dioxide and PM-10 = particulate matter smaller than 10 micrometers in effective diameter. Maintenance areas (previous nonattainment areas) are also listed by pollutant in the EPA Green Book.
Detailed maps showing maintenance areas by county (entire county as red, partial county as yellow) are available for all pollutants combined and the following individual criteria pollutants:
Carbon monoxide
Lead
Nitrogen dioxide
Ozone (1-hour)
Particulate matter (PM-10)
Sulfur dioxide
| Background Documents |
As last amended in 1990, the Clean Air Act (section 176(c)) requires that no Federal agency "shall engage in, support in any way or provide financial assistance for, license or permit, or approve, any activity which does not conform to an implementation plan ..." and that "the assurance of conformity to such an implementation plan shall be an affirmative responsibility of the head of ..." the Federal agency. In essence, each Federal agency must demonstrate that every decision or action it takes will comply with applicable air quality requirements.
Conformity to an implementation plan means: (1) complying with an implementation plan's purpose of eliminating or reducing the severity and number of violations of the national ambient air quality standards, and achieving expeditious attainment of such standards; and (2) assuring that such activities will not: (a) cause or contribute to any new violation of any standard in any area; (b) increase the frequency or severity of any existing violation of any standard in any area; or (c) delay timely attainment of any standard or any required interim emission reductions or other milestones in any area.
The Clean Air Act further separated Federal highway and transit actions ("transportation conformity") from all other Federal actions ("general conformity"). In order to establish Federal regulations to implement the "general conformity" requirements, EPA published draft regulations in the Federal Register on March 15, 1993 (58 FR 13835-68). Based on public review and comment, the final "general conformity" regulations were also published in the Federal Register (pdf) (58 FR 63213-59, dated November 30, 1993). Both the "general conformity" and "transportation conformity" regulations have been codified at 40 CFR 93 - Determining Conformity of Federal Actions to State or Federal Implementation Plans (pdf).
Although the Air Quality Conformity analysis and determination process required by the Clean Air Act is separate from the Environmental Impact Assessment process required under the National Environmental Policy Act, these two processes may be combined when desired. An example of how these processes may be combined is available (pdf).
Numerous staff are available to assist Federal Land Management agencies with air quality technical issues. Air quality staff are listed by agency: USDA-Forest Service (pdf), USDI-Bureau of Land Management (pdf), USDI-National Park Service (pdf) and USDI-U.S. Fish & Wildlife Service (pdf) .
Finally, a list of Local, State, Tribal and Federal Air Regulatory Agencies is provided to assist in determining implementation plan requirements and area boundaries (i.e.; nonattainment, maintenance, etc.) for site-specific conformity evaluations and determinations.
Content manager - Scott Archer (scott_archer@blm.gov)