EPA has released the final report, Integrated Science Assessment (ISA) for Oxides of Nitrogen and Sulfur - Ecological Criteria. This final ISA document represents a concise synthesis and evaluation of the most policy-relevant science and will ultimately provide the scientific bases for EPA's decision on retaining or revising the current secondary standards for NO₂ and SO₂.

Oxides of nitrogen and oxides of sulfur are two of six principal (or criteria) pollutants for which EPA has established national ambient air quality standards (NAAQS). The Clean Air Act requires EPA to periodically review the scientific basis for these standards by preparing an Integrated Science Assessment (ISA), formerly called an Air Quality Criteria Document (AQCD). The previous AQCDs for oxides of nitrogen and sulfur were released in 1993 and 1982, respectively.

This ISA was prepared as part of the joint review of the secondary or welfare-based NAAQS for oxides of nitrogen and sulfur. The ISA evaluates and integrates the newly available environmental evidence, and contains the key information and judgments formerly found in the AQCD. A series of Annexes to the ISA provides more extensive and detailed summaries of the most pertinent scientific literature.

This is EPA’s latest evaluation of the scientific literature on the potential adverse environmental effects resulting from exposures to oxides of nitrogen and sulfur. There are significant new data, particularly with regards to acidification and nitrogen enrichment, that strengthen the evidence for these effects since the last scientific review documents were released.

U.S. EPA. 2008 Final Report: Integrated Science Assessment (ISA) for Oxides of Nitrogen and Sulfur Ecological Criteria. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-08/082F, 2008.