Regional and background aerosol trace elemental composition observed in eastern Canada

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Abstract
Measurements of the trace elemental composition of atmospheric aerosols were undertaken at three rural locations in eastern Canada during the autumn of 1984. One aim was to investigate differences in anthropogenic elemental composition between aerosols of regional eastern North American origin and “background” aerosols in air masses moving into the region. Another aim was to identify the origin of aerosol trace elements with the use of air parcel back-trajectories, multivariate analysis, and lead isotope ratios. Daily aerosol samples taken at Dorset Ontario, For& Montmorency Quebec, and Kejimkujik Nova Scotia, were analyzed by instrumental neutron activation analysis and inductively-coupled plasma mass spectrometry for Ti, Br, Mn, In, Na, V, Al, Ca, Se, As, Sb, Pb, Cd, and Pb-206/207 isotope ratios. Average concentrations of Na and V showed the greatest regional diversity and were 8.0 and 5.4 times higher at Kejimkujik than at Dorset, respectively. Factor analysis revealed the presence of a soil, a marine, and a general pollution component in the aerosols, plus additional components specific for a few elements of anthropogenic origin. Cornparison of mean concentrations in samples grouped by similarity of the associated back-trajectories showed that In and As were excellent tracers of non-ferrous smelter emissions. Trajectories from prominent coal-burning areas were also enriched in As but were associated with low In concentrations. Groups of trajectories originating from background areas, i.e., without major anthropogenic sources of aerosols, formed a significant fraction of the samples and accounted for 20%-25% of the classified aerosol samples at each site. Comparison of the mean concentrations in the background groups with each other and with similar aerosol data from the Arctic showed that both local influences, such as the composition of soils in the immediate area, and long-range transport of aerosols can affect the apparent local composition of the background aerosol. Using recent findings by Sturges and Barrie that there is a significant difference between the Pb isotope ratio in aerosols from smelters, Canadian auto exhaust and American sources, the fraction of Pb originating from each source was estimated for each location. During the 3-month period studied, it is estimated that Pb from automotive emissions in the US accounted for 46%, 28%, and 44% of the atmospheric Pb at Dorset, For& Montmorency, and Kejimkujik, respectively, versus 52%, 67%, and 51% from Canadian auto exhaust. DOI: 10.1111/j.1600-0889.1988.tb00116.x