1. Environmental Health Science and Research Bureau, Health Canada, Ottawa, Ontario, Canada
2. Health Analysis Division, Statistics Canada, Ottawa, Ontario, Canada
3. Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
4. Department of Medicine, McGill University, Montreal, Quebec, Canada
5. Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
6. School of Public Health, University of California–Berkeley, Berkeley, California, USA
7. Department of Economics, Brigham Young University, Provo, Utah, USA
8. School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada
9. Air Quality Research Division, Environment Canada, Downsview, Ontario, Canada
10. Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA