1. Department of Chemistry and Department of Physical and Environmental Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario, Canada M1C 1A4, National Water Research Institute, 867 Lakeshore Road, Burlington, Ontario, Canada L7R 4A6, and Centre for Atmospheric Research Experiments, Meteorological Service of Canada, 6248 Eighth Line, Egbert, Ontario, Canada L0L 1N0