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Under the Clean Air Act, the EPA is required to review and, if appropriate, revise the air quality criteria and national ambient air quality standards (NAAQS) every 5 years. On April 3, 2012, the EPA published a final rule in which the Agency determined to retain the current secondary standards (welfare-based) for nitrogen oxides (NOx) and for sulfur oxides (SOx). On January 15, 2013, the EPA published a final rule in which the Agency retained the secondary standards for particulate matter. The current review of the air quality criteria and secondary standards for ecological effects of SOx, NOx and particulate matter includes the preparation of an Integrated Science Assessment and a Policy Assessment by the EPA, with opportunities for review by the EPA's Clean Air Scientific Advisory Committee (CASAC) and the public. These documents will inform the Administrator's proposed decision as to whether to retain or revise the standards. The proposed decision would be published in the Federal Register with opportunity provided for public comment. The Administrator’s final decisions would take into consideration these documents, CASAC advice, and public comment on the proposed decision. Opportunities for public engagement and sharing of information concerning this NAAQS review will include public hearings, tribal consultation, informational meetings, and through the CASAC public meetings.

Statement of Need: Under the Clean Air Act Amendments of 1977, EPA is required to review and if appropriate revise the air quality criteria and national ambient air quality standards (NAAQS) every 5 years. On April 3, 2012, EPA published a final rule retaining the Secondary NAAQS for NO2 and SO2, without revision. On August 29, 2013, EPA announced that it is reviewing the April 2012 decision on the secondary air quality standards for NO2 and SO2. On December 3, 2014, EPA announced it is reviewing the secondary air quality standards for particulate matter.

Summary of the Legal Basis: Under the Clean Air Act Amendments of 1977, EPA is required to review and if appropriate revise the air quality criteria and the primary (health-based) and secondary (welfare-based) national ambient air quality standards (NAAQS) every 5 years.

Alternatives: The main alternatives for the Administrator’s decision on the review of the secondary national ambient air quality standards for NOx, SOx and PM include retaining or revising the existing standards.

Anticipated Costs and Benefits: When the Agency proposes revisions to the standards, the Agency prepares a Regulatory Impact Analysis (RIA) to provide the public with illustrative estimates of the potential costs and health and welfare benefits of attaining the revised standards. However, 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.

Risks: The review builds on the review of the NOx and SOx NAAQS, completed in 2012, and includes preparation by EPA of an Integrated Review Plan, an Integrated Science Assessment, and a Policy Assessment, which includes a risk/exposure assessment, with opportunities for review by the EPA's Clean Air Scientific Advisory Committee (CASAC) and the public. The final versions of these documents will inform the Administrator's proposed decisions on whether to revise or retain the Secondary NOx SOx and PM NAAQS. The Administrator’s final decisions on whether to revise or retain the Secondary NOx SOx and PM NAAQS will take into consideration the scientific evidence and quantitative analyses presented in these documents, CASAC advice, and public comment on the proposed decision.