Under the Clean Air Act Amendments of 1977, EPA is required to review, and if appropriate, revise the air quality criteria for the primary (health-based) and secondary (welfare-based) national ambient air quality standards (NAAQS) every five years. On January 13, 2013, the EPA published a final rule revising the NAAQS for particulate matter to provide increased protection for public health. The current review includes the preparation of an Integrated Review Plan, an Integrated Science Assessment and, if warranted, a Risk/Exposure Assessment, and also a Policy Assessment by EPA, with opportunities for review by EPA's Clean Air Scientific Advisory Committee and the public. These documents will inform the Administrator's proposed decision as to whether to retain or revise the standards. This proposed decision will be published in the Federal Register with opportunity provided for public comment. The Administrator's final decisions will take into consideration these documents and public comment on the proposed decision.