CHEMICAL-COMPOSITION OF THE ATMOSPHERIC AEROSOL IN THE TROPOSPHERE OVER THE HUDSON-BAY LOWLANDS AND QUEBEC-LABRADOR REGIONS OF CANADA

Atmospheric aerosols were collected in the boundary layer and free tro posphere over continental and coastal subarctic regions of Canada duri ng the July-August 1990 joint U.S.-Canadian Arctic Boundary Layer Expe dition (ABLE) 3B/Northern Wetlands Study (NOWES). The samples were ana lyzed for the following water soluble species: Sulfate, nitrate, ammon ium, potassium, sodium, chloride, oxalate, methylsulfonate, and total amine nitrogen. Ammonium and sulfate were the major water soluble comp onents of these aerosols. The nearly neutral (overall) chemical compos ition of summertime aerosol particles contrasts their strongly acidic wintertime composition. Aerosol samples were separated into several ai r mass categories and characterized in terms of chemical composition, associated mixing ratios of gaseous compounds, and meteorological para meters. The fundamental category represented particles associated with ''background'' air masses. The summertime atmospheric aerosols in bac kground air over the North American subarctic and Arctic regions were characterized by relatively small and spatially uniform mixing ratios of the measured species. These aerosol particles were aged to the exte nt that they had lost their primary source signature. The chemical pro file of the background air aerosols was frequently modified by additio ns from biomass fire plumes, aged tropical marine air, and intrusions of upper tropospheric/lower stratospheric air. Aerosols in boundary la yer background air over the boreal forested region of Quebec-Labrador had significantly larger mixing ratios of ammonium and sulfate relativ e to the Hudson Bay region. This may reflect infiltration of anthropog enic pollution or be due to natural emissions from this region.