To embed, copy and paste the code into your website or blog: Congress addressed the issue of interstate transport of air pollution in the Clean Air Act by enacting a “Good Neighbor Provision.” That provision requires upwind states to eliminate their contributions to air pollution in downwind states. EPA has promulgated various rules to implement the Good Neighbor Provision, beginning with the NOx Budget Trading Program and including the Clean Air Interstate Rule and, most recently, the Cross-State Air Pollution Rule (CSAPR). These rulemakings address the interstate transportation of ozone. CSAPR is updated regularly to align with the current ozone National Ambient Air Quality Standard (NAAQS). In response to various legal challenges and to update CSAPR with respect to the 2008 ozone NAAQS, EPA amended CSAPR in 2016. In 2019, the D.C. Circuit in