On October 30, 2020, EPA published in the Federal Register a proposed rule to revise its 2016 Cross-State Air Pollution Rule Update (the CSAPR Update) to further reduce interstate air pollution from 12 upwind states. EPA is proposing this revision pursuant to its authority under the Clean Air Act’s “Good Neighbor” provision (section 110(a)(2)(D)(i)(l)), which requires upwind states to prevent sources located within their borders from contributing significantly to nonattainment or interfering with maintenance, of the national ambient air quality standards (NAAQS) in downwind states.