On February 24, 2021, the U.S. Environmental Protection Agency (EPA) sent for White House Office of Management and Budget (OMB) prepublication review the agency’s final rule addressing “good neighbor” obligations under the 2008 national ambient air quality standards (NAAQS) for ozone. The rulemaking responds to the U.S. Court of Appeals for the D.C. Circuit’s 2019 ruling remanding the Cross-State Air Pollution Rule (CSAPR) in Wisconsin v. EPA. As discussed in Sidley’s prior blog post, on October 15, 2020, EPA issued its proposal. EPA is under a court-ordered deadline to promulgate its final rule by March 15, 2021. See New Jersey, et al. v. Wheeler, No. 1:20-cv-01425 (S.D.N.Y. 2020). Although OMB review typically takes 60 to 90 days, the most recent Unified Agenda indicates that the final rule will be published in March, in line with the court-ordered deadline. Under this timeline, it is possible that the revised rule goes into effect this year, potentially including the proposed rule’s new or revised federal implementation plans for 12 states and more stringent emission reduction requirements for the upcoming NOx (nitrogen oxides) ozone seasons.