Chemical Composition of Organic Aerosols and the Origin of Organic Particulate Matter in Southern Ontario Air

Measurements of potential molecular markers, polycyclic aromatic hydrocarbons (PAHs), hopanes and aromatic acids, for particulate matter from vehicle exhaust were conducted as part of the Southern Ontario Aerosol study (SONTAS 2000) in the summer of 2000. In this field study, 29 PM₁₀ high-volume samples were collected in downtown Hamilton where traffic and industrial sources are expected to dominate the emissions into the atmosphere. Additionally 34 PM₁₀ samples were collected at Simcoe, a rural site located 80 km southwest of Hamilton and about 150 -200 km north and northeast of several other major, densely populated urban areas in the U.S. In order to allow comparison with direct vehicular emissions, four studies were conducted in the York Gateway tunnel in downtown Toronto. Each PM₁₀ sample was analyzed by GC/MS for five, six and seven- ring PAHs, one sterane, four hopanes, and n-alkanes from C20 to C34, and by capillary electrophoresis for ten aromatic acids and one nitrophenol. The Hamilton and the tunnel measurements show strong correlations among several hopanes, PAHs and cholestane, indicating that in downtown Hamilton engine exhaust is the dominant source for these molecular markers. However, at the rural site, the correlation between hopane series and PAH series is very weak, while the correlations among individual PAHs are still excellent. This indicates that engine exhaust alone cannot explain the observations of these molecular markers at the rural location. Similarly, the observations of aromatic acids in downtown Hamilton and rural southern Ontario cannot be explained by a direct impact from vehicular emissions alone. Other potential sources are coal burning power plants, agricultural waste burning, and formation of secondary organic aerosols from gas phase precursors.