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The Plain English Guide to the Clean Air Act

Interstate and International Air Pollution

Air Pollution Travels Long Distances
  • Toxaphene, a pesticide used in the U. S. corn belt has been found in fatty tissues of polar bears and other Arctic animals - thousands of miles from any possible source.
  • Nitrogen oxides deposited from the air have contributed to fish kills by increasing the growth of oxygen-depleting algae in the Chesapeake Bay. Over a quarter of the nitrogen in the Bay and its tidal rivers and streams is estimated to come from air pollution carried by the wind from power plants and industrial sources far away.
  • Emissions of sulfur oxides from power plants in the Midwest contribute to acid rain, haze and particle pollution problems in the eastern United States hundreds of miles away.

Air pollution does not recognize state or international boundaries. Pollutants can be carried long distances by the wind. Dirty air even turns up in places where you least expect it, like national parks or wilderness areas in remote parts of the United States.

Taller smokestacks can lift pollutants high above a local community but help pollutants get into wind currents that can carry them hundreds, even thousands, of miles. For example, emissions from power plants and industrial boilers can travel hundreds of miles and contribute to smog, haze, and air pollution in downwind states. One family of pollutants, nitrogen oxides, also reacts with other chemicals, sunlight and heat to form ground-level ozone. The nitrogen oxides and the ozone itself can be transported with the weather to help cause unhealthy air in cities and towns far downwind.

States and tribes seeking to clean up air pollution are sometimes unable to meet EPA's national standards because of pollution blowing in from other areas. The Clean Air Act has a number of programs designed to reduce long-range transport of pollution from one area to another. The Act has provisions designed to ensure that emissions from one state are not contributing to public health problems in downwind states. It does this, in part, by requiring that each state's implementation plan contain provisions to prevent the emissions from the facilities or sources within its borders from contributing significantly to air pollution problems "downwind" - specifically in those areas that fail to meet EPA's national air quality standards. If a state or tribe has not developed the necessary plan to address this downwind pollution, EPA can require the state to do so. If the state still does not take the necessary action, EPA can implement a federal plan to achieve the necessary emission reductions.

Also, the Act gives any state or tribe the authority to ask EPA to set emission limits for specific sources of pollution in other (upwind) areas that significantly contribute to its air quality problems. States and tribes can petition EPA to require the upwind areas to reduce air pollution.

The Act provides for interstate commissions to develop regional strategies for cleaning up air pollution. For instance, state and tribal governments from Maine to Virginia, the government of the District of Columbia, and EPA are working together through the Ozone Transport Commission (OTC) to reduce ground-level ozone along the east coast.

The Clean Air Act also requires EPA to work with states to reduce the regional haze that affects visibility in 156 national parks and wilderness areas, including the Grand Canyon, Yosemite, the Great Smokies, and Shenandoah National Parks. During much of the year in these areas, a veil of white or brown haze hangs in the air blurring the view. Most of this haze is not natural. It is air pollution, carried by the wind often many hundreds of miles from where it originated. Under the regional haze provisions of the Clean Air Act, the states and tribes, in coordination with the EPA, the National Park Service, U.S. Fish and Wildlife Service, the U.S. Forest Service, and others, develop and implement air quality protection plans to reduce the pollution that causes visibility impairment. EPA has worked with states and tribes across the country to form Regional Planning Organizations to develop plans to reduce pollutants that cause haze.

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