This proposed rule would address Clean Air Act requirements concerning the transport of air pollution across state boundaries. This action would address concerns raised by the D.C. Circuit in its decision remanding the Clean Air Interstate Rule and will potentially be influenced by the outcome of the Cross-State Air Pollution Rule litigation. It is the next step for the EPA to move forward with the states to address interstate transport with respect to the 2008 ozone National Ambient Air Quality Standards. This rule proposes to define upwind states' obligations under the 2008 ozone standards to address transported air pollution affecting the eastern half of the U.S. However, this action will not address the particulate matter National Ambient Air Quality Standards.