Environment Canada, in cooperation with the Ontario Ministry of Environment and the Walpole Island Indian Band, has been conducting an air monitoring study in a region of southern Ontario near Detroit. Two sampling sites are located in the city of Windsor, Ontario. The Windsor sites are frequently downwind of the numerous emission sources of the greater Detroit area, which include coke ovens, iron and steel industry, incinerators, power generation facilities, lime and cement operations, and automotive assembly plants. The Windsor sites are also influenced by the regional background of secondary sulfate common in the eastern U.S. and Canada, as well as by automobile emissions. Fine and coarse particle samples were collected on Teflon filters with a dichotomous sampler. Samples were analyzed by energy-dispersive X-ray fluorescence (XRF) at the U.S. EPA, Research Triangle Park facility. A subset of the samples were selected for analysis by scanning electron microscopy combined with energy-dispersive XRF (SEM/EDX). Morphological features of the particles combined with chemical data have been shown to be useful in resolving source types which cannot be resolved by conventional means.