Eight northeastern states are again suing the Environmental Protection Agency (EPA) to force the agency to slash emissions of nitrogen oxides (NO_x) and volatile organic compounds (VOCs) blowing in from power plants and other sources in nine “upwind” Midwestern and southern states.

The Ozone Transport Region, which was established by Congress under Section 184 of the Clean Air Act, currently includes 11 “downwind” states: Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont.

Most of these states have rules or fall under a federal mandate to directly or indirectly require sources achieve reductions of NO_x and VOCs, which contribute to the formation of ozone. In 2014—the most recent year for which the National Emissions Inventory (NEI) is available—about 56% of NO_x emissions in the U.S. came from on-road and non-road mobile sources. Electric generating units accounted for about 13% of NO_x emissions nationwide. The bulk of VOCs emitted were from industrial processes, including solvents (48%) and mobile sources (27%).…

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