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

Nitrogen Dioxide- Health Criteria

Oxides of Nitrogen (NOx) (Primary - Health Criteria) Report Cover
(PDF, 260 pp, 18 MB,
About PDF)

The Issue
Nitrogen dioxide (NO2) is one of a group of highly reactive gases known as "oxides of nitrogen," or "nitrogen oxides (NOx)." Other nitrogen oxides include nitrous acid and nitric acid. EPA’s National Ambient Air Quality Standard uses NO2as the indicator for the larger group of nitrogen oxides. NO2 forms quickly from emissions from cars, trucks and buses, power plants, and off-road equipment. In addition to contributing to the formation of ground-level ozone, and fine particle pollution, NO2 is linked with a number of adverse effects on the respiratory system.

EPA Action
EPA's NOx and SOx research efforts are focused on improving emissions estimates, determining health and ecological effects, and improving modeling capabilities. The Clean Air Act requires EPA to periodically review the science for six major air pollutants, including NOx and SOx. EPA's National Center for Environmental Assessment develops Integrated Science Assessments (ISAs) that summarize the science related to the health and ecological effects caused by these pollutants. ISAs provide a comprehensive review of the policy-relevant scientific literature published since the last National Ambient Air Quality (NAAQS) review and are a critical part of the scientific basis for establishing the NAAQS.

In 2008, EPA released the Integrated Science Assessment for Oxides of Nitrogen- Health Criteria (Final) and the Integrated Science Assessment for Sulfur - Health Criteria (Final). But because of the overlap of these 2 air pollutants in the environment, the reports were combined into a single ecological criteria report, called the Integrated Science Assessment for Oxides of Nitrogen and Sulfur - Ecological Criteria (Final). [See the history of the pollutant reports for more detailed information on the NOx/SOx assessments]

[Update] EPA is announcing the availability of the Second External Review Draft of the Integrated Science Assessment for Oxides of Nitrogen – Health Criteria for public comment and independent peer review. This report, when finalized, will serve as the scientific basis for review of the primary (health-based) National Ambient Air Quality Standard for nitrogen dioxide. [Federal Register Notice January 30, 2015]

Workshop announcement:

  • TBD: EPA released the second draft NOx ISA document to seek review by the Clean Air Scientific Advisory Committee (CASAC) and the public (the peer review meeting date and location will be announced in a separate Federal Register notice).

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