CHARACTERIZATION OF THE SOUTHWESTERN DESERT AEROSOL, MEADVIEW, AZ

Sulfate, organic carbon, and soil dust were the major components of th e fine aerosol at Meadview, AZ, during the summer of 1992. Sulfate mas s median diameters (typically 0.15-0.27 mu m) were much smaller than m ass median diameters for organic carbon (typically 0.43-0.83 mu m). Or ganic carbon size distributions were broader and more varied. Intersam pler comparisons show that sulfur and sulfate measurement technology p rovided precise and relatively accurate (within 2-22%) concentrations. However, large differences were observed between IMPROVE filter and M OUDI impactor carbon concentrations. This is indicative of the large u ncertainties with which carbon concentrations are measured. The IMPROV E backup filter subtraction procedure was partially responsible for th ese differences. Meadview sulfate was not completely neutralized by am monium; SO2 concentrations were comparable to sulfate concentrations; and virtually all of the nitrate was present as gas-phase nitric acid. Our estimates suggest that primary organic aerosol from urban areas a ccounts for no more than 24% on average of the organic aerosol found a t Meadview, AZ. The remainder is most likely secondary and biogenic OC , as well as OC from local and regional anthropogenic sources.