Integrated Science Assessment (ISA) for Oxides of Nitrogen and Sulfur Environmental Criteria (First External Review Draft)

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 scientific review documents for oxides of nitrogen and sulfur were released in 1993 and 1982, respectively.

This draft ISA was prepared as part of the joint review of the secondary or welfare-based NAAQS for oxides of nitrogen and sulfur. The draft 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 draft 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.

In April 2008, the first draft ISA will be reviewed by the Clean Air Scientific Advisory Committee (CASAC) at a public meeting in Research Triangle Park, NC. A second draft ISA will be released in summer 2008, which will address CASAC and public comments received on the first draft ISA. The final ISA will be posted on the EPA Web site to provide the scientific bases for EPA’s periodic review and possible revision of the secondary NAAQS for oxides of nitrogen and sulfur. The final ISA is expected by mid-December 2008.