Proposed rule · 2026-04339

Air Plan Approval; Arizona; Attainment Plan for the Hayden SO2 Nonattainment Area for the 1971 and 2010 Sulfur Dioxide National Ambient Air Quality Standards

The Environmental Protection Agency (EPA) is proposing to approve revisions to the Arizona state implementation plan (SIP) for attaining the 1971 and 2010 sulfur dioxide (SO<INF>2</INF>) national ambient air quality standards (NAAQS or "standards") in the Hayden SO<INF>2</INF> nonattainment area. These SIP revisions, collectively referred to as the "Hayden SO<INF>2</INF> Plan" or "Plan," include Arizona's attainment demonstration and other elements required under Clean Air Act (CAA or "Act") sections 110, 172, 191, and 192. In addition to an attainment demonstration, the revisions address the requirements for meeting reasonable further progress (RFP) toward attainment of the NAAQS, reasonably available control measures and reasonably available control technology (RACM/RACT), base-year and projection-year emissions inventories, nonattainment new source review (NSR), emissions limitations necessary to provide for attainment, and contingency measures. The EPA is proposing to approve the SIP revisions as meeting the CAA requirements. This action is being taken under the CAA. We are taking comments on this proposal and plan to follow with a final action.