Interstate Transport of Air Pollution

September 27, 2017: Maryland files suit against EPA under Clean Air Act

Maryland filed suit against the Environmental Protection Agency for its failure to act on a petition requiring power plants in five upwind states to reduce pollution that significantly affects the quality of the air that Marylanders breathe.


July 20, 2017: Maryland's Letter to EPA Related to Petition 126


November 16, 2016: Maryland Petitions EPA to Reduce Air Pollution from Upwind States

The petition, filed by the Maryland Department of the Environment under Section 126 of the federal Clean Air Act, asks that the U.S. Environmental Protection Agency require 36 power plant units in the upwind states (Indiana, Kentucky, Ohio, Pennsylvania and West Virginia) to run their air pollution controls to reduce emissions. The petition includes data that shows that these power plants have stopped running their pollution controls effectively. A requirement to run those controls throughout the summer “ozone season” is identical to what Maryland’s largest coal-fired power plants must do under regulations implemented last year by the Hogan Administration.

The Section 126 petition

Section 126 of the federal Clean Air Act gives a state the authority to ask EPA to find that specific sources of air pollution in other states are significantly contributing to non-attainment or interfering with maintenance of federal air quality standards in the petitioning state. The Clean Air Act allows 60 days for EPA to respond to these types of petitions. To read the Appendices for the petition, please click here.


Research shows those 36 out-of-state power plant units emit pollution that contributes at times to poor air quality in Maryland, the petition states. Though Maryland has made dramatic progress on air quality in recent years, emissions from out-of-state sources could prevent Maryland from attaining and maintaining federal health-based air quality standards.

Ground-level ozone, or smog, has been one of Maryland’s most pervasive and challenging air pollution problems. About 70 percent of Maryland’s ozone problem originates from emissions in upwind states. Parts of some downwind states, including Maryland, would remain in violation of federal air quality standards even if they eliminated all of the pollution generated within their borders.

For the past three years, Maryland has been working in partnership with about 25 other eastern and Midwestern states to solve this problem. This State Collaborative on Ozone Transport (SCOOT) effort has focused on ensuring that large coal-fired power plants that have purchased pollution controls run those controls when ozone is a problem. Under current laws, many power plants in upwind states can operate without the controls running and nonetheless comply with their long-term pollution limits.

Last year, environmental officials from SCOOT states asked power plants in their states to increase the use of their controls for nitrogen oxides (NOx), which help to form ozone. This voluntary approach did not work.

Other legal steps have been taken to reduce ozone transport. Maryland has also joined other states in petitioning EPA to add nine upwind states to the Ozone Transport Region. If added to the Ozone Transport Region, those states would be required to take additional steps to reduce air pollution that has been found to significantly affect downwind states.

Maryland Works to Reduce In-state Pollution

Meanwhile, Maryland addressed this problem by implementing regulations that require the state’s largest coal-fired power plants to optimize their air pollution controls to minimize NOx emissions during the summer ozone season. That requirement went into effect in 2015. The regulations also include requirements for longer-term reductions of pollution from power plants.

Maryland’s air quality has improved significantly in recent years. Reductions in emissions from utilities, motor vehicles and others sources as diverse as manufacturing and consumer products have reduced the number of days on which Marylanders breathe poor air. Maryland is very close to meeting all federal air quality standards. The state is also close to meeting a more stringent ozone standard established last year. Reduced emissions from upwind states could determine whether Maryland remains in compliance with the prior ozone standard and whether the state meets the newer, more stringent standard.


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