1. Centre for Atmospheric Research Experiments, Science and Technology Branch, Environment Canada, 6248 Eighth Line, Egbert, Ontario L0L 1N0, Canada, Norwegian Institute for Air Research, Polar Environmental Centre, NO-9296 Tromsø, Norway, Department of Environmental Assessment, Swedish University of Agricultural Sciences, P.O. Box 7050, SE-705-07, Uppsala, Sweden, Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ontario M5S 3E5, Canada, and...