Cross-State Air Pollution Rule (CSAPR)

On July 6, 2011 the U.S. Environmental Protection Agency (EPA) finalized the Cross-State Air Pollution Rule (CSAPR) to address air pollution from upwind states that crosses state lines and affects air quality in downwind states. Sulfur dioxide (SO2) and oxides of nitrogen (NOX) emissions react in the atmosphere and contribute to the formation of fine particle (soot) pollution. NOX also contributes to ground-level ozone (smog) formation. These emissions and the soot and smog they form can affect air quality and public health locally, regionally, and in states hundreds of miles downwind.  For more information on interstate transport of air pollution, see EPA’s interstate air transport page.


This rule requires certain states in the eastern half of the U.S. to improve air quality by reducing power plant emissions that cross state lines and contribute to smog and soot pollution in downwind states. These improvements help downwind areas attain and maintain EPA’s health-based soot and smog air quality standards known as National Ambient Air Quality Standards (NAAQS).


The Cross-State Air Pollution Rule replaced EPA’s 2005 Clean Air Interstate Rule (CAIR), following the direction of a 2008 court decision that required EPA to issue a replacement regulation.  CSAPR implementation began on January 1, 2015.

On September 7, 2016, the EPA revised the CSAPR ozone season NOX program by finalizing an update to CSAPR for the 2008 ozone National Ambient Air Quality Standards, known as the CSAPR Update. The CSAPR Update ozone season NOX program will largely replace the original CSAPR ozone season NOX program starting on May 1, 2017. The CSAPR Update will further reduce summertime NOX emissions from power plants in the eastern U.S.


IEA Supports the Midwest Ozone Group


For many years, the IEA has been an active participant of the Midwest Ozone Group (MOG). The IEA participated in the development of comments that MOG offered on the Indiana Proposed Good Neighbor State Implementation Plan (SIP).