On October 15, the U.S. Environmental Protection Agency (EPA) proposed to update its Cross-State Air Pollution Rule (CSAPR) for the 2008 ozone national ambient air quality standard (NAAQS) requiring further reduction in emissions of nitrogen oxides (NOx) from power plants in 12 states. The agency is proposing to require the added emissions reduction to come from optimization of existing selective catalytic reduction controls for the 2021 ozone season and installation or upgrade of low NOx burners for the 2022 ozone season. EPA identified that NOx emissions from the 12 states are expected to contribute at or above a threshold of 1% of the 2008 NAAQS ozone level, that is, 0.75 ppb, while the projected NOx emissions from the remaining nine of the 21 states subject to the CSAPR do not contribute significantly to nonattainment in downwind states, for which the agency thus proposes no further obligations. The proposed rulemaking was EPA’s response to the U.S. Court of Appeals for the D.C. Circuit’s decision in Wisconsin v. EPA, which remanded the 2016 CSAPR update to the agency for failing to satisfy the “good neighbor” obligations under the Clean Air Act to meet the 2008 ozone NAAQS, as discussed here. EPA is under a court order to finalize this proposal by March 15, 2021. EPA will hold a public hearing, and public comments will be due 45 days after the proposal is published in the Federal Register.