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PSD Overview

The Clean Air Act (CAA) includes measures to prevent significant deterioration of air quality (PSD) in areas where air quality is better than the national standards established by the Environmental Protection Agency (EPA) to protect public health and welfare. One of the express purposes of the PSD program is "to preserve, protect, and enhance the air quality in national parks, national wilderness areas, national monuments, national seashores, and other areas of special natural, recreational, scenic, or historic value." In general, "clean air areas" are protected through ceilings on additional amounts of certain air pollutants over a baseline level. The PSD "increments" vary based on classification of the area.

Congress gave the greatest degree of air quality protection to certain national parks and wilderness areas. These "Class I" areas include areas designated as national parks or national wilderness areas as of August 7, 1977, that are greater than 6,000 acres (parks) or 5,000 acres (wilderness). There are 48 units of the National Park System, 21 units of the National Wildlife Refuge System, and 88 U.S. Forest Service Wilderness Areas designated as Class I. Only a small amount of new pollution is allowed in these Class I areas. All other clean air regions are Class II areas, unless redesignated by states or tribes, with moderate pollution increases allowed.

In addition to the PSD increments, there are special mechanisms for protecting Class I area resources that might be affected by air pollution. These "air quality related values", or "AQRVs", include visibility, vegetation, lakes and streams, soils, fish, animals, and monuments. The CAA gave the Federal land managers (FLMs) an affirmative responsibility to protect AQRVs. Congress specifically established a national goal of preventing any future and remedying any existing human-caused visibility impairment in congressionally-designated Class I areas. States are required to make reasonable progress toward this national goal. EPA visibility protection regulations are designed to stimulate a return to natural visibility conditions over a 60 year period.

One of the ways Congress chose to protect clean air was through preconstruction review of major sources of air pollution. People wishing to build new, or significantly modify existing, facilities in clean air regions must obtain a prevention of significant deterioration (PSD) permit from the state, tribe or EPA and meet certain requirements generally designed to minimize air quality deterioration. In all cases, permit applicants must agree to install the best available control technology and demonstrate that their emissions will not cause a violation of the national ambient air quality standards or a PSD increment.

For more information about the Clean Air Act visit our Law & Policy web pages.

updated on 07/21/2010  I   http://nature.nps.gov/air/Permits/index.cfm   I  Email: Webmaster