1. Meteorological Service of Canada, Environment Canada, 4905 Dufferin Street, Toronto, ON M3H 5T4, Canada, Environmental Science Department, Lancaster University, Lancaster, LA1 4YQ, U.K., AirZOne, 2240 Speakman Drive, Mississauga, ON L5K 1A9, Canada, and Freshwater Institute, 501 University Crescent, Winnipeg, MB R3T 2N6, Canada