1. Polar Environmental Centre, Norwegian Institute of Air Research, Tromsø NO-9296 Norway, Department of Chemistry, University of Alberta Edmonton, Alberta T6G 2G2, Canada, Department of Laboratory Medicine and Pathology, University of Alberta Edmonton, Alberta T6G 2G3, Canada, and Richardson College for the Environment, Environmental Studies Program and Department of Chemistry, University of Winnipeg, Winnipeg Manitoba R3B 2E9