Setting National Ambient Air Quality Standards (NAAQS) is an action that is at the core of the Clean Air Act. NAAQS apply to "criteria" pollutants—pollutants that "endanger public health or welfare," and whose presence in ambient air "results from numerous or diverse mobile or stationary sources." Six pollutants are currently identified as criteria pollutants. The EPA Administrator can add to the list if he determines that additional pollutants meet the act's criteria, or delete them if he concludes that they no longer do so. NAAQS do not directly regulate emissions. Rather, the primary NAAQS identify pollutant concentrations in ambient air that must be attained to protect public health with an adequate margin of safety; secondary NAAQS identify concentrations necessary to protect public welfare, a broad term that includes damage to crops, vegetation, property, building materials, etc. In essence, NAAQS are standards that define what EPA considers to be clean air. Their importance stems from the long and complicated implementation process that is set in motion by their establishment. Once NAAQS have been set, EPA, using monitoring data and other information submitted by the states, identifies a list of areas that exceed the standards and must, therefore, reduce pollutant concentrations to achieve them. State and local governments then have three years to produce State Implementation Plans which outline the measures they will implement to reduce the pollution levels in these "nonattainment" areas. EPA also acts to control many of the NAAQS pollutants wherever they are emitted through national standards for products that emit them (particularly mobile sources, such as automobiles) and emission standards for new stationary sources, such as power plants. Because the understanding of pollution's effects changes with new research, the Clean Air Act requires that EPA review NAAQS at five-year intervals and revise them as may be appropriate. To ensure that these reviews meet the highest scientific standards, the 1977 amendments to the act required the Administrator to appoint an independent Clean Air Scientific Advisory Committee (CASAC). CASAC has seven members, largely from academia and from private research institutions, who generally serve for two consecutive three-year terms. In conducting NAAQS reviews, their expertise is supplemented by panels of the nation's leading experts on the health and environmental effects of the specific pollutants that are under review. These panels can be quite large. The recent particulate matter and ozone review panels, for example, had 22 and 23 members, respectively. CASAC, as well as the public, makes suggestions regarding the membership of these panels, with the final selections made by EPA. The panels review the agency's work during NAAQS-setting and NAAQS-revision, rather than conducting their own independent reviews. CASAC panels had a nearly 30-year history of working quietly in the background, advising the agency's staff on NAAQS reviews, and issuing what were called "closure letters" on the agency documents that summarize the science and the policy options behind the NAAQS. Closure letters have been used by CASAC panels to indicate a consensus that the agency staff's work provides an adequate scientific basis for regulatory decisions. The science and policy documents, written by EPA staff, generally have gone through several iterations before the scientists were satisfied, but, with the issuance of a closure letter, CASAC has in past years removed itself from the process, leaving the formal proposal and final choice of standards to the Administrator. Proposal comes in the form of a Federal Register notice that triggers a formal public comment period, and the final choice is promulgated in the Federal Register , as well, following the review of public comments. In 2006, the usual pattern of NAAQS reviews was upset by three events. First, as EPA promulgated revisions to the particulate matter (PM) NAAQS, CASAC and its PM Review Panel publicly objected both to the Administrator's decision not to strengthen the annual standard for fine particulates (PM 2.5 ) and to various aspects of his decision regarding larger particles (PM 10 ). The committee took the unprecedented steps of writing to the Administrator both after he proposed the standards in January, and after he promulgated them in September. In the latter communication, CASAC stated unanimously that the Administrator's action " does not provide an ' adequate margin of safety ... requisite to protect the public health ' (as required by the Clean Air Act) ...." (Italics in original.) A month after CASAC's challenge to the final particulate decision, CASAC's ozone review panel took an unusually strong stand regarding review of that NAAQS. The panel approved EPA's policy options paper (or "Staff Paper"), the next-to-last formal step before the Administrator proposes revision of the ozone NAAQS, but in doing so it stated, "There is no scientific justification for retaining the current primary 8-hr NAAQS ...," and it recommended a range for the revised standard that would be substantially more stringent than the current standard. The Administrator proposed a revision generally outside CASAC's range on June 20, 2007, and in March 2008 he promulgated new ozone standards that were outside CASAC's range. The 2006 actions by CASAC and its ozone and PM review panels were followed in short order by an EPA announcement, December 7, 2006, that it would modify the process for setting and reviewing NAAQS. Under EPA's new procedures, the agency's political appointees have a role early in the process, helping to choose the scientific studies to be reviewed, and CASAC will no longer have a role in approving the policy Staff Paper with its recommendations to the Administrator. (The Staff Paper will also be renamed, becoming a "Policy Assessment.") CASAC will be relegated to commenting on the paper after it appears in the Federal Register , during a public comment period. The goal, according to agency officials, is to speed up the review process, which has consistently taken longer than the five years allowed by statute. "These improvements will help the agency meet the goal of reviewing each NAAQS on a five-year cycle as required by the Clean Air Act, without compromising the scientific integrity of the process," according to the memorandum that finalized the changes. The changes caused concern among environmental groups and some in the scientific community, however, because, they say, they give a larger role to the agency's political appointees and a smaller role to EPA staff and CASAC. These three events (CASAC's challenge of the PM NAAQS, its panel's unusually forceful stance regarding revision of the ozone NAAQS, and EPA's decision to change the NAAQS review process) have thrust CASAC, heretofore a relatively obscure scientific committee, into the limelight. The developments raise important questions regarding the role of science and scientists in the setting of air quality standards. The Senate Environment and Public Works Committee included CASAC issues among those it considered February 6, 2007, in a hearing on "Oversight of Recent EPA Decisions." The House Oversight and Government Reform Committee plans a hearing on the ozone standard April 24, 2008. To provide a better understanding of the issues, this report provides a history of the NAAQS-setting process and the role of CASAC since its inception in the late 1970s. It also reviews various proposals for change that have been discussed, including EPA's December 2006 modifications. Prior to enactment of the Clean Air Act of 1970, there was no authority for the establishment of national ambient air quality standards. Control of air pollution and standards for air quality were considered primarily a state's right and responsibility. Beginning in 1963, however, Congress began establishing the framework for what became the NAAQS-setting process. The Clean Air Act of 1963 (P.L. 88-206) and the Air Quality Act of 1967 (P.L. 90-148) directed the Secretary of Health, Education, and Welfare to "develop and issue to the States such criteria of air quality as in his judgment may be requisite for the protection of the public health and welfare." These criteria were to be issued "after consultation with appropriate advisory committees and Federal departments and agencies," and were to "accurately reflect the latest scientific knowledge useful in indicating the kind and extent of all identifiable effects on health and welfare...." To provide scientific advice, the Surgeon General established a National Air Quality Criteria Advisory Committee (NAQCAC) in March 1968. Establishment of the NAAQS Process . The air quality criteria were originally intended primarily to assist the states in establishing their own air quality standards; but they survive today as the first step in the establishment of national standards (NAAQS). NAAQS themselves were first required by the Clean Air Act Amendments of 1970 (P.L. 91-604). The 1970 amendments directed the new Environmental Protection Agency (which had taken over the air pollution functions of the Health, Education, and Welfare Department) to promulgate NAAQS for each pollutant for which air quality criteria had already been issued, and to promulgate NAAQS with respect to any additional air pollutant for which criteria would be issued after the date of enactment. Primary NAAQS, as described in Section 109(b)(1), were to be "ambient air quality standards the attainment and maintenance of which in the judgment of the Administrator, based on such criteria and allowing an adequate margin of safety, are requisite to protect the public health." Secondary standards (which, in practice, are often the same as the primary) were also to be based on the criteria and set at a level "requisite to protect the public welfare from any known or anticipated adverse effects" (Section 109(b)(2)). The Administrator was permitted to revise both types of standards. Establishing Formal Review Requirements: SAB and ERDDAA . To assist the Administrator in setting criteria, the Advisory Committee established by the Surgeon General in 1968 (NAQCAC) was transferred to EPA in 1970, as part of the Reorganization Plan that established EPA, but it had no statutory authority.