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Air Quality: EPA's Integrated Science Assessments (ISAs)

Basic Information

What is an Integrated Science Assessment?

Integrated Science Assessments (ISA) are reports that represent a concise evaluation and synthesis of the most policy-relevant science for reviewing the National Ambient Air Quality Standards (NAAQS). EPA has set NAAQS for six principal pollutants, which include: ozone, particulate matter, carbon monoxide, sulfur dioxides, nitrogen oxides, and lead. Called criteria pollutants, these are derived from numerous sources and are considered harmful to public health and the environment.

The ISA accurately reflects “the latest scientific knowledge useful in indicating the kind and extent of identifiable effects on public health which may be expected from the presence of [a] pollutant in ambient air” (42 U.S.C. 7408). Because the ISA communicates critical science judgments relevant to the NAAQS review, it forms the scientific foundation for the review of the NAAQS standards. Key information and judgments formerly contained in previously released assessments, referred to as Air Quality Criteria Documents (AQCD), are incorporated in these new ISA assessments. Additional details of the pertinent scientific literature published since the last review, as well as selected older studies of particular interest, are included in a the supporting appendices of the ISA. Thereby the ISA serves to update and revise the evaluation of the scientific evidence available at the time of the previous review of the NAAQS to the newest studies and information.

Lastly, all ISAs are vetted through a rigorous peer review process, including review by the Clean Air Scientific Advisory Council and public comment periods.


History of the Pollutant Reports

  • 1970: The Clean Air Act of 1970 established and required periodic review of two types of standards that limit permissible amounts of the criteria pollutants. Primary standards set limits to protect public health, including the health of sensitive populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect against visibility impairment, damage to ecosystems and to animals, crops, vegetation, and buildings. [The Plain English Guide to the Clean Air Act]

Carbon Monoxide (CO)

Lead (Pb)

Oxides of Nitrogen and Sulfur (NOx/SOx)– Ecological Criteria

Nitrogen Oxides (NOx)– Health Criteria

Sulfur Oxides (SOx) - Health Criteria

Ozone and related Photochemical Oxidants

Particulate Matter

Legislative Requirements

In particular, EPA's National Center for Environmental Assessment (NCEA) leads the effort to periodically review the science upon which the NAAQS are based by producing Integrated Science Assessments (ISA) [see Integrated Science Assessments (ISA) Legislative Requirements for more information] of these 6 pollutants. The ISA is a concise review, synthesis, and evaluation of the most policy-relevant science, and communicates critical science judgments relevant to the NAAQS review. Two sections of the Clean Air Act (CAA, the Act) govern the establishment and revision of the NAAQS.

  • Section 108 of the Act (42 U.S.C. 7408) directs the Administrator to identify and list “air pollutants” that “in [her] judgment, may reasonably be anticipated to endanger public health and welfare” and whose “presence … in the ambient air results from numerous or diverse mobile or stationary sources” and to issue air quality criteria for those that are listed (42 U.S.C. 7408). Air quality criteria are intended to “accurately reflect the latest scientific knowledge useful in indicating the kind and extent of identifiable effects on public health or welfare which may be expected from the presence of [a] pollutant in ambient air…” 42 U.S.C. 7408(b).
  • Section 109 of the Act (42 U.S.C. 7409) directs the EPA Administrator to propose and promulgate “primary” and “secondary” National Ambient Air Quality Standards (NAAQS) for pollutants listed under Section 108. Section 109(b)(1) defines a primary standard as one “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.” A secondary standard, as defined in Section 109(b)(2), must “specify a level of air quality the attainment and maintenance of which, in the judgment of the U.S. EPA Administrator, based on such criteria, is required to protect the public welfare from any known or anticipated adverse effects associated with the presence of [the] pollutant in the ambient air.” The requirement that primary standards include an adequate margin of safety was intended to address uncertainties associated with inconclusive scientific and technical information available at the time of standard setting. It was also intended to provide a reasonable degree of protection against hazards that research has not yet identified. These uncertainties are components of the risk associated with pollution at levels below those at which human health effects can be said to occur with reasonable scientific certainty. Thus, in selecting primary standards that include an adequate margin of safety, the Administrator is seeking not only to prevent pollution levels that have been demonstrated to be harmful, but also to prevent lower pollutant levels that may pose an unacceptable risk of harm, even if the risk is not precisely identified as to nature or degree.

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