Identification of PM2.5 Sources in Regions along the Windsor to Montreal Corridor

Cheol-Heon Jeong (1), Maygan L. McGuire (1), Greg J. Evans (1), Dennis Herod (2), Tom Dann (3), Ewa Dabek-Zlotorzynska (3), Daniel Wang (3), Luyi Ding (3), Valbona Celo (3), David Mathieu (3)

(1) Southern Ontario Centre for Atmospheric Aerosol Research, University of Toronto, Toronto, Ontario, Canada (2) Air Emissions Priorities Division, Environment Canada, Gatineau, Quebec, Canada (3) Environmental Science and Technology Branch, Environment Canada, Ottawa, Ontario, Canada

     Abstract Number: 670
     Last modified: May 14, 2010

Abstract
The Windsor to Montreal corridor which runs approximately 850 km alongside Lake Erie and Lake Ontario represents one of the most densely populated areas in Canada. In order to evaluate the contributions of common sources of PM2.5, source apportionment analyses were performed using a receptor model, Positive Matrix Factorization (PMF) for urban and rural areas; Windsor (urban), Simcoe (rural), Toronto (urban), St. Anicet (rural), Montreal (urban). Wind direction and back trajectory analyses were performed to determine influences of local and regional sources. Among the PMF-resolved PM2.5 sources, the highest rural-urban difference was observed in the contributions of secondary nitrate; the Toronto nitrate factor was ~37% higher than the nitrate factor in Simcoe. However, the nitrate contribution in Simcoe was higher than the Montreal nitrate contributions. This indicates that air quality in this rural area was strongly impacted by regional scale nitrate sources. Back trajectory analyses for these nitrate factors in Simcoe and St. Anicet supported the influence of regional scale nitrate transported from Ohio and Indiana to the Windsor to Montreal corridor. The secondary sulphate contributions at these urban sites were ~10% higher than the corresponding rural sites, indicating that regional contributions for the secondary sulphate are important in the air quality well upwind of the border. While there was no statistical difference in the EC-rich factor between Simcoe and Toronto, the EC-rich factor in Simcoe was much higher than the contributions in Montreal and St. Anicet, supporting the fact that the EC-rich factor was strongly related to regional combustion sources. Air quality in the rural area near the U.S. border in southern Ontario was significantly influenced by regional scale pollutants and their contributions were much larger than the contribution of local sources found in Toronto and Montreal. The comparisons of PM2.5 sources in urban and rural areas will provide important information about ambient pollutant control strategies for trans-boundary pollution between Canada and the U.S.