Policy Assessment for the Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur, February 2011 Version

摘要

This Policy Assessment has been prepared by staff in the Environmental Protection Agencys (EPA) Office of Air Quality Planning and Standards (OAQPS) in conjunction with the Agencys ongoing joint review of the secondary (welfare-based) national ambient air quality standards (NAAQS) for oxides of nitrogen and sulfur. This Policy Assessment evaluates the policy implications of the key scientific information contained in the Integrated Science Assessment (ISA) for Oxides of Nitrogen and Sulfur-Ecological Criteria, prepared by EPAs National Center for Environmental Assessment (NCEA), results from the analyses contained in the Risk and Exposure Assessment (REA) for Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur, as well as additional staff analyses conducted for and presented in this document. It presents staff conclusions regarding the adequacy of the current NO2 and SO2 secondary standards as well as alternative standards for consideration in this review. This Policy Assessment is intended to help bridge the gap between the relevant scientific and technical information and the judgments required of the EPA Administrator in determining whether, and if so, how, it is appropriate to revise the secondary NAAQS for oxides of nitrogen and sulfur. This Policy Assessment considers the available scientific evidence and quantitative risk-based analyses, together with related limitations and uncertainties, and focuses on the basic elements of air quality standards: indicator, averaging time, form, and level. These elements, which serve to define each standard, must be considered collectively in evaluating the public welfare protection afforded by the standards.