crs_reports: R49350

Congressional Research Service reports with summaries, authors, and topic classifications.

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R49350 National Ambient Air Quality Standards and Selected Issues for Congress 2026-09-14T04:00:00Z 2026-09-16T09:25:12Z Active Reports Jonathan D. Haskett, Omar M. Hammad National Ambient Air Quality Standards (NAAQS), Air Quality Congress passed the Clean Air Act Amendments of 1970 to provide “a more effective program to improve the quality of the Nation’s air.” This legislation included provisions that helped regulate criteria air pollutants present nationwide in the ambient (outdoor) air, based on the criteria that they were a danger to public health or welfare and were emitted from “numerous diverse mobile or stationary sources.” The U.S. Environmental Protection Agency (EPA) has designated six criteria air pollutants: particulate matter (PM), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), and lead (Pb). For each of these pollutants EPA has established primary and secondary National Ambient Air Quality Standards (NAAQS), uniform nationwide standards that define EPA air quality goals. EPA sets standards at a level requisite to prevent adverse effects, including for sensitive populations, with an adequate margin of safety. EPA is precluded from considering cost when establishing or revising a NAAQS, but NAAQS determinations can affect pollution control costs; State Implementation Plans (SIPs), which outline states’ control strategies to achieve or maintain compliance with air quality standards; and individual facility emissions permits—as well as morbidity and mortality. To ensure that air pollution from new or expanded stationary criteria-air-pollution emissions sources is sufficiently controlled so an area can attain and maintain the new or revised NAAQS, EPA and the states administer the New Source Review (NSR) permitting program. The NSR program requires preconstruction air permits for new or modified sources such as petroleum refineries and chemical plants. The NSR program includes a minor NSR program required for minor new sources or minor modifications at existing sources that do not exceed certain emissions thresholds, a Prevention of Significant Deterioration (PSD) NSR program required for new major sources or major modifications at existing sources in attainment areas, and a nonattainment NSR program for new major sources or major modifications at existing sources in nonattainment areas. When EPA establishes a new or revised NAAQS, it triggers a sequential regulatory process requiring air permitting agencies to base new PSD permits on the new or revised NAAQS; states and tribes to submit recommendations on whether areas should be designated attainment/unclassifiable or nonattainment with respect to achieving air quality goals; EPA to evaluate these recommendations and notify states and tribes of agreement or disagreement; EPA to designate areas as attainment/unclassifiable or nonattainment; states to submit infrastructure SIPs showing they have the necessary programs and authorities to meet the new or revised NAAQS; areas in nonattainment to submit SIPs demonstrating attainment of the new or revised NAAQS within a certain time frame; and a demonstration of transportation conformity for nonattainment areas indicating that federally funded transportation projects in the areas are consistent with SIP air pollution control goals. Some Members of Congress have taken an interest in several issues related to NAAQS. These include the timing of the NAAQS regulatory stages, the influence of external pollution sources on the NAAQS-based designation process, and the promulgation of more stringent PM2.5 NAAQS. Legislation has been introduced to lengthen the NAAQS review cycle and change the timing of preconstruction permitting. Legislation has also been introduced to ensure that pollution from outside an area, either natural or anthropogenic (i.e., caused by humans), cannot affect an area’s attainment status. In addition, EPA promulgated more stringent primary annual PM2.5 NAAQS in 2024. Some Members have opposed this change and have introduced legislation to disapprove of it under the Congressional Review Act, while other Members have approved of it and have sent a letter to EPA expressing this support. https://www.congress.gov/crs_external_products/R/PDF/R49350/R49350.3.pdf https://www.congress.gov/crs_external_products/R/HTML/R49350.html

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