Learn About the ISAs

What is an Integrated Science Assessment?

Integrated Science Assessments (ISA) are reports that represent concise evaluations and syntheses 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 dioxide, nitrogen dioxide, and lead. Numerous sources emit these "criteria air pollutants", which are considered harmful to public health and the environment.

The Integrated Science Assessment is intended to "accurately reflect the latest scientific knowledge useful in indicating the kind and extent of identifiable effects on public health and welfare which may be expected from the presence of [a] pollutant in the ambient air” [42 U.S.C. 7408(b)]. Because the Integrated Science Assessment communicates critical science judgments relevant to the NAAQS review, it forms the scientific foundation for the review of the NAAQS standards. All Integrated Science Assessments are vetted through a rigorous peer review process, including review by the Clean Air Scientific Advisory Committee and public comment periods. The process of developing Integrated Science Assessments, including literature review and evaluation, integration of evidence, and characterization of evidence for public health and welfare impacts of criteria air pollutants, is described in the Preamble to the Integrated Science Assessments.

Does the ISA include the NAAQS Standards?

No, these can be found at reviewing national ambient air quality standards (NAAQS): scientific and technical information.

How can I get more involved?

EPA sends out federal register notices (FRN) when the public is invited to comment on ISA draft reports prior to external peer review. In addition the EPA Science Advisory Board (SAB) often post other ways for public involvement in advisory activities.

How do I comment on the current review drafts?

EPA will announce the availability of each draft ISA in the FRN with detailed steps on how to comment on the report. Typically drafts are released 30-days in advance of the external peer review meeting to allow the public to review and send in comments. All comments can be submitted to the Regulations.gov Web site under the docket ID number listed in the announcement and on the ISA website. The docket submissions are then collected and sent to the reviewers prior to the peer review meeting for the discussion. All drafts (first, second, and third) will be filed under the same docket ID for continuity.

History of the Integrated Science Assessments


2008 - Present

Based on recommendations from the peer review of draft reports done in 2005/6, EPA switched from releasing full Air Quality Criteria Documents (AQCD) to releasing the Integrated Science Assessments (ISAs). The ISAs then referenced key information and judgements formally contained in the older AQCDs and began to add pertinent new scientific literature published since the last review.
2008 As part of changes to the National Ambient Air Quality Standards (NAAQS), EPA developed and launched the HERO application. Beginning with a revision to the NAAQS review process, EPA was tasked with creating a "more detailed and comprehensive science assessment support document, which will eventually be linked to an electronic database of scientific studies." HERO was launched as the back-bone of the AQCDs replacing long bibliographic lists that made up the studies. This greatly streamlined the development of future assessments.
1970 - 2006 EPA released numerous draft and final Air Quality Criteria Documents (AQCDs) (see individual criteria sub-pages for specific milestones and links).
1977 EPA released an update to an AQCD in response to specific requirements of Section 108 of the Clean Air Act, as amended in 1977.
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.
1969 EPA published the first two ACQDs for particulate matter and sulfur oxides.

Legislative Requirements

Two sections of the Clean Air Act (CAA, the Act) govern the establishment and revision of the NAAQS. See the process of reviewing the NAAQS for additional information.

  • 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