1. Environment Canada, Air Quality Processes Research Section, Toronto, Ontario M3H 5T4, Canada
2. Swedish University of Agricultural Sciences (SLU), Department of Aquatic Sciences and Assessment, Uppsala, Uppland SE-750 07, Sweden
3. Ontario Ministry of the Environment, 125 Resources Road, Toronto, Ontario M9P 3V6, Canada
4. University of Toronto, Department of Chemistry, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada