Protecting visibility: the key to preventing significant deterioration in Western air quality

The protection of visibility, including atmospheric discoloration and visual clarity as well as visual range, is now seen to be the key to protecting air quality in the west. Legislation to this end has directed the Environmental Protection Agency and Federal land managers to protect air quality from new emission sources, and to correct existing sources of impairment. Major points of the 1977 Clean Air Act Amendments are examined in terms of scope and scheduling for implementation, which remain unclear. The legislative history of air pollution control is reviewed, and the economic implications of as-yet-unsolved technological requirements are noted.