This action is a revised response to a 2016 Clean Air Act section 126(b) petition from Maryland. The petition requests that the EPA make a finding that emissions from 36 power plants in five states adversely influence air quality in Maryland. The EPA denied the petition in 2018. The action was challenged, and the D.C. Circuit remanded the EPA's denial as to four power plants that Maryland identified that have a selective non-catalytic reduction emissions control device (Maryland v. Environmental Protection Agency No. 18-1285 (D.C. Cir. 2020)). This action addresses the court's remand and provides a revised response to the petition.