US EPA

EPA announced the availability of the final report, Integrated Science Assessment (ISA) for Oxides of Nitrogen and Sulfur - Ecological Criteria. This 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 oxides of nitrogen (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.

The intent of the ISA, according to the CAA, is to “accurately reflect the latest scientific knowledge expected from the presence of [a] pollutant in ambient air” (U.S. Code, 1970a, 1970b). It includes scientific research from atmospheric sciences, exposure and deposition, biogeochemistry, hydrology, soil science, marine science, plant physiology, animal physiology, and ecology conducted at multiple scales (e.g., population, community, ecosystem, landscape levels). Key information and judgments formerly found in the Air Quality Criteria Documents (AQCDs) for NOX and SOX are included; Annexes provide a more detailed discussion of the most pertinent scientific literature. Together, the ISA and Annexes serve to update and revise the last NOX and SOX AQCDs which were published in 1993 and 1982, respectively.

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

On December 22, 2008, an updated version of the ISA was posted to this site. In this updated version, the Executive Summary has been revised stylistically and graphics resolution has been adjusted in the ISA. No substantive changes have been made to the document. In addition, the Executive Summary and individual ISA and Annex chapters have been posted as separate files.