Risk and Exposure Assessment for Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur. First Draft, Chapters 1-6

摘要

The U.S. Environmental Protection Agency (EPA) is conducting a joint review of the existing secondary (welfare-based) National Ambient Air Quality Standards (NAAQS) for nitrogen oxides (NOx) and sulfur oxides (SOx), which are currently defined in terms of nitrogen dioxide (NO2) and sulfur dioxide (SO2), respectively. Sections 108 and 109 of the Clean Air Act (CAA or the Act) govern the establishment and periodic review of the NAAQS and of the air quality criteria upon which the standards are based. The NAAQS are established for pollutants that may reasonably be anticipated to endanger public health or welfare and whose presence in the ambient air results from numerous or diverse mobile or stationary sources. The NAAQS are based on air quality criteria that reflect the latest scientific knowledge, useful in indicating the kind and extent of identifiable effects on public health or welfare that may be expected from the presence of the pollutant in ambient air. Based on periodic reviews of the air quality criteria and standards, EPA makes revisions to the criteria and standards and promulgates any new standards as may be appropriate. The Act also requires that an independent scientific review committee advise the Administrator as part of this NAAQS review process, a function now performed by the Clean Air Scientific Advisory Committee (CASAC).