ATMOSPHERIC AEROSOL OVER ALASKA - 1 - SPATIAL AND SEASONAL VARIABILITY

Aerosol chemical composition data for seven National Park Service loca tions in Alaska for the period from 1986 to 1995 were analyzed. Data f or elements, black carbon, and total mass were obtained for samples of atmospheric particles less than 2.5 mu m in diameter. Assuming that a ll elemental aerosol S was from SO4=, concentrations of excess (nonmar ine) sulfate (XSO4=) were calculated by subtraction of the sea salt SO 4= mass fraction to Na and observed Na concentrations. Mass concentrat ion of XSO4= ranged from 0.01 to 3.9 mu g m(-3), and mass concentratio n of black carbon (BC) ranged from 0.01 to 5 mu g m(-3). Seasonal vari ations with maxima during the winter/spring season and minima in the s ummer for most of the sites in Alaska were observed for the XSO4= but not for the BC and the fine mass concentration. The seasonal variation s of XSO4= concentration were always higher in northwestern Alaska. BC concentration in central Alaska peaked during the summertime because of the high BC emission from forest fires. The Pb concentration in cen tral Alaska shows a negative trend over the timescale of measurements. It is concluded that all of the sites experience aerosol pollution fr om long distance, regional, and local sources. Seasonal variations of the XSO4= concentration are related to the seasonal variations in long -range transport of midlatitudinal S emissions, to the varying rate of photochemical SO4= fine aerosol production and to fine aerosol remova l processes in the troposphere. The spatial distribution of XSO4= show s a strong northwest to southeast negative gradient that can be associ ated with the long-range transport of anthropogenic aerosol from pollu tion sources located to the north or northwest of Alaska.