(a) Approval. On April 21, 1997, the Iowa Department of Natural Resources (IDNR) submitted a maintenance plan and redesignation request for the Muscatine County nonattainment area for the 1971 SO2 national ambient air quality standard (NAAQS). The maintenance plan and redesignation request satisfy all applicable requirements of the Clean Air Act.

(b) Determination of attainment by the attainment date. As of May 9, 2022, the EPA has determined that the Muscatine, Iowa SO2 nonattainment area has attained the 2010 1-hour SO2 primary NAAQS by the applicable attainment date of October 4, 2018.

(c) Redesignation to attainment. EPA has determined, as of November 18, 2025, that the Muscatine County 2010 SO2 nonattainment area is redesignated to attainment of the 2010 SO2 1-hour National Ambient Air Quality Standard (NAAQS) in accordance with the requirements of Clean Air Act (CAA) section 107(d)(3) and has approved its maintenance plan and supplemental modeling demonstration analyses as meeting the requirements of CAA section 175A.