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Statement of Need: As established in the Clean Air Act, the national ambient air quality standards for oxides of nitrogen and oxides of sulfur are to be reviewed every 5 years.

Summary of the Legal Basis: Section 109 of the Clean Air Act (42 U.S.C. 7409) directs the Administrator to propose and promulgate "primary" and "secondary" national ambient air quality standards for pollutants identified under section 108 (the "criteria" pollutants). The "primary" standards are established for the protection of public health, while "secondary" standards are to protect against public welfare.

Alternatives: The main alternatives for the Administrator's decision on the review of the national ambient air quality standards for oxides of nitrogen and oxides of sulfur are whether to retain or revise the existing standards.

Anticipated Costs and Benefits: The Clean Air Act makes clear that the economic and technical feasibility of attaining standards are not to be considered in setting or revising the NAAQS, although such factors may be considered in the development of State plans to implement the standards. Accordingly, the Agency prepares cost and benefit information in order to provide States information that may be useful in considering different implementation strategies for meeting proposed or final standards. Cost and benefit information is not developed to support a NAAQS rulemaking until sufficient policy and scientific information is available to narrow potential options for the form and level associated with any potential revisions to the standard. Therefore, work on the developing the plan for conducting the cost and benefit analysis will generally start 1 1/2 to 2 years following the start of a NAAQS review.

Risks: During the course of this review, risk assessments may be conducted to evaluate public welfare risks associated with retention or revision of the NOx/SOx secondary standards.