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, N oxides and particulate matter included 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 informed the Administrator's proposed decision to strengthen the secondary NAAQS for sulfur oxides (SOx) to 10-15 ppb, as an annual average, averaged over 3 years; while proposing to retain existing secondary standards for nitrogen oxides (N oxides) and particulate matter (PM). The proposed decision was published in the Federal Register with opportunity provided for public comment. Opportunities for public engagement and sharing of information concerning this NAAQS review include public hearings, tribal consultation, informational meetings, and CASAC public meetings. The Administrator’s final decisions will take into consideration published documents, CASAC advice, and public comment on the proposed decision. EPA is under a consent decree for this review to sign the final rule by December 10, 2024.