The Clean Air Act includes a Good Neighbor Provision, which requires states to prohibit their own sources of pollution from emitting in quantities that “contribute significantly” to another state’s inability to achieve national ambient air quality standards. When upwind states fail to abide by this requirement, the Act authorizes downwind states to petition the Environmental Protection Agency (EPA) for relief.
In 2018, EPA denied five such petitions filed by Maryland and Delaware, which sought tighter limits on ozone-forming emissions from power plants in Indiana, Kentucky, Ohio, Pennsylvania, and West Virginia. Maryland and Delaware, supported by other states and a coalition of environmental groups, have now challenged those denials in the U.S. Court of Appeals for the D.C. Circuit. In our amicus brief supporting the challenges, we focused on EPA’s erroneous claim that no further emission reductions at the specified plants would be cost-effective.