1. Department of Chemistry, The University of British Columbia, Vancouver, V6T 1Z1 British Columbia, Canada
2. Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen 5232, Switzerland
3. Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
4. Now at College of Ecology and Environment, Xinjiang University, Ürümqi 830017, China