ON THE POTENTIAL OF REGIONAL-SCALE EMISSIONS ZONING AS AN AIR-QUALITYMANAGEMENT TOOL FOR THE GRAND-CANYON

Air arriving at the Grand Canyon of the Colorado River during 1988-198 9 is attributed to one of four geographic quadrants-NE, SE, SW, NW-on the basis of routinely calculated back-trajectories. Most of the haze observed at the Canyon is attributed to the SW quadrant, which contain s the populous and industrialized areas of southern California. Air fr om either northern quadrant tends to be significantly clearer than air from either southern quadrant. Clear northern air is most common duri ng the winter, and is rarely observed during the summer tourist season , when steady flow from the southwest is the norm. Various possible in terpretations of these empirical results are discussed, with varying i mplications for emissions management policy.