1. Air Quality Research Division, Science and Technology Branch, Environment Canada, 2121 Trans Canada Highway, Dorval, Quebec, Canada H9P 1J3, Belgian Institute for Space Aeronomy (BIRA-IASB), 3 Avenue Circulaire, B-1180 Brussels, Belgium, Air Quality Research Division, Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, Canada M3H 5T4, and Departments of Atmospheric & Oceanic Sciences, and Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec,...