IDENTIFICATION OF CANDIDATE CLEAN-AIR CORRIDORS FOR THE COLORADO PLATEAU

The U.S. Clean Air Act, amended in 1990, mandated the establishment of the Grand Canyon Visibility Transport Commission (GCVTC). The commiss ion is required to submit a report to the U.S. Environmental Protectio n Agency addressing visibility issues in the region, including ''the e stablishment of clean air corridors, in which additional restrictions on increases in emissions may be appropriate to protect visibility in affected Class I areas.'' This paper presents a methodology to identif y candidate geographic areas for consideration for Clean Air Corridor (CAC) status for Colorado Plateau Class I areas. The methodology uses thousands of model determined trajectories over a five year pe riod (1 988 to 1992) to indicate the paths taken by air that arrives during cl ean air conditions at Class I areas. These clean air back-trajectories identify upwind areas where pollution emissions could jeopardize curr ently pristine visibility. Using this methodology, six candidate areas are identified, ranging in size from 75,000 to 506,000 square miles, and permitting varying levels of visibility protection for clean air d ays at Grand Canyon, Canyonlands, and Petrified Forest National Parks. Assuming effective emissions management of the CAC, the larger the CA C, the greater the visibility protection during clean air conditions.