The Clean Air Act gives special air quality and visibility protection to national parks larger than 6,000 acres and national wilderness areas larger than 5,000 acres that were in existence when it was amended in 1977. These are “Class I” areas. All other areas are “Class II” allowing for a moderate amount of air quality deterioration. Because air pollution is often regional in nature, reductions in pollution to improve visibility in Class I parks will also improve visibility in all parks in the surrounding area. Class I areas are managed by the National Park Service, U.S. Fish and Wildlife Service, U.S. Forest Service, and several Native American Tribes.
The Clean Air Act outlines procedures that a State or Tribal governing body may use to redesignate areas as either Class I (greater air quality protection) or Class III (less protection). However, mandatory Class I areas may not be redesignated and Class II "floor" areas may not be redesignated to Class III. Prior to proposing a redesignation, the redesignating authority must analyze and describe the health, environmental, economic, social, and energy effects of the redesignation.
National Park Service
- Alphabetical listing of all NPS Class I areas
- Park specific air quality information
- Map of NPS Class I areas (png, 1.4 MB)
- NPS Class I boundary file in ArcView shapefile format (zip, 1.4 MB)