EPA's regional haze regulations call for states to establish goals for improving visibility in national parks and scenic areas. Affected areas, called Class I areas, are defined by the Clean Air Act as areas designated as of August 1977 that meet any of the following criteria:

•  national parks greater than 6,000 acres,

•  wilderness areas and national memorial parks greater than 5,000 acres,

•  international parks.

There are 156 Class I areas nationwide, including many of our best-known and most-treasured national parks such as Acadia, Everglades, Grand Canyon, Great Smoky Mountains, Mount Rainier, Shenandoah, Yellowstone, and Yosemite.