Regional Haze/Particulate Matter
Regional haze is the "dirty-looking" air that prevents us from seeing clearly or very far through the air. It especially affects our enjoyment of national parks, such as the Grand Canyon and the Great Smoky Mountains. Sulfate particles, formed by the reaction of sulfur dioxide (SO2) from power plants and other sources in the atmosphere, account for 50 to 70 percent of the visibility reduction in the eastern part of the U.S. Both sulfate and nitrate particles (resulting from nitrogen oxides (NOx) emissions) affect visibility in the western U.S.
The Acid Rain Program is expected to improve the visual range in the eastern U.S. by 30 percent by cutting SO2 emissions from electric utilities by 50 percent from 1980 levels. Based on a study of the value national park visitors place on visibility, the visual range improvements expected at national parks in the eastern U.S. due to the Acid Rain Program's SO2 reductions will be worth over a billion dollars annually by the year 2010. In the western part of the U.S., nitrates and carbon also play roles, but sulfates have been implicated as an important source of visibility impairment in many of the Colorado River Plateau national parks, including the Grand Canyon, Canyonlands, and Bryce Canyon.For more information about EPA's other efforts to reduce regional haze, visit EPA's Visibility Web site.