1. Public Health Ontario, Toronto, Ontario, Canada
2. Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
3. Population Studies Division, Health Canada, Ottawa, Ontario, Canada
4. Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada
5. Department of Family and Community Medicine, University of Toronto, Toronto, Ontario, Canada
6. Department of Medicine, McGill University, Montreal, Quebec, Canada
7. Division of Clinical Epidemiology, McGill University Health Centre, Montreal, Quebec, Canada
8. Division of Cardiovascular Medicine, University of Michigan Medical School, Ann Arbor, Michigan, USA
9. Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
10. Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, Berkeley, California, USA
11. Harvard–Smithsonian Centre for Astrophysics, Cambridge, Massachusetts, USA
12. Air Quality Research Division, Environment Canada, Toronto, Ontario, Canada