PATTERNS OF DUST TRANSPORT TO THE GRAND-CANYON

Dust particles in the 2.5 mu m to 15 mu m diameter range contribute to regional haze that sometimes impairs visibility at the Grand Canyon a nd other National Parks in the southwestern U.S. The proportion of air borne dust that is attributable to land modification is unknown, but c an be expected to increase as a consequence of the region's rapid popu lation growth. This note examines the upwind histories of air masses b ringing high coarse-particle concentrations to the Grand Canyon over a five-year monitoring period. Although arid and semi-arid lands extend in all directions, and the fastest airflows generally have a northerl y component, high dust concentrations are most common in air arriving from the southwest, where development has been concentrated. This empi rical association suggests that the expansion of suburban and agricult ural lands is raising dust levels at the Grand Canyon.