| Abstract
| - The chemical composition of Toronto PM2.5 was measureddaily from Feb 2000 to Feb 2001, and source apportionmentwas undertaken using positive matrix factorization (PMF).In Toronto, PM2.5 levels were influenced both by localurban activities and also by regional-scale transport. Althoughseveral PMF solutions were possible, an eight-sourcemodel for explaining the observed Toronto PM2.5 was foundto provide realistic results and interesting insights intosources. The four main sources were coal combustionrelated to regional transport and secondary sulfate (26%),secondary nitrate related to both local and upwindsources of NOx and NH3 (36%), secondary organic aerosols(SOA) formed from a variety of precursor organic emissions(15%), and motor vehicle traffic (10%). The other detectablesources were road salt (winter) and three types of primaryPM2.5 hypothesized to be associated with smelters, coaland oil combustion, industry, and local construction. Overall,motor vehicle-related emissions (including road salt andnitrate) were estimated to be responsible for about 40% ofthe PM2.5. In the summer, the SOA mass was estimatedto contribute ∼20% to the PM2.5. Inclusion of water-soluble,low-molecular-weight organic acids led to identificationof this component, thus providing a significant improvementin PMF's ability to resolve sources. Without organic acidmeasurements the SOA portion of the observed PM2.5 wasassigned to the secondary coal component, increasingits contribution and resulting in a source profile with anunrealistic amount of organic mass. This suggests that inthe northeastern part of North America, there are physicaland/or chemical processes that lead to close interactionbetween secondary organic and inorganic aerosols.
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