A SYNOPTIC CLIMATOLOGICAL ANALYSIS OF AIR-QUALITY IN THE GRAND-CANYON NATIONAL-PARK

Daily air quality variations within the Grand Canyon National Park, AZ are related to a regional synoptic climatology. The climatology is developed using upper air data from 21 stations throughout the western U.S.A. and Mexico from 1979 to 1988. Thirteen synoptic situations are identified which represent days with distinct and recurring meteorological conditions throughout the region. Daily particulate concentrations and scattering coefficient readings from Hopi Point, on the south rim of the Grand Canyon, are related to the daily synoptic climatology. Three synoptic situations are associated with poor air quality. Summer monsoon days have poor air quality because of high humidity and cloud cover. On continental high days, a slow-moving anticyclone is located near the Great Basin and local pollutants are trapped within the boundary layer in this poorly ventilated air mass. The situation with the worst air quality-Rockies Ridge-has strong southwesterly winds throughout the troposphere, suggesting that regional haze is advected from southern California into the Grand Canyon area. Good air quality occurs (1) during zonal flow situations when the jet stream is strong; (2) when cold, dry air masses are present; (3) during dry and generally clear days in the summer. This research demonstrates the utility of analysing air quality problems from a synoptic climatological framework.