Jun Meng, Dalhousie University, Dept Physics & Atmospheric Sci, Halifax, NS, Canada, Chi Li, University of California at Berkeley, Dept Chemistry, Berkeley, United States, Randall Martin, Washington University in St. Louis, Energy, Environmental & Chemical Engineering, St. Louis, United States, Aaron van Donkelaar, Dalhousie University, Dept Physics & Atmospheric Science, Halifax, NS, Canada, Perry Hystad, University of Oregon, Eugene, United States and Michael Brauer, University of British Columbia, School of Population and Public Health, Vancouver, BC, Canada