1. Air Quality Research Branch, Meteorological Service of Canada, Toronto, Ontario, Canada, and Institute of Earth Environment, Chinese Academy of Sciences, Xian, China
2. Centre for Atmosphere Watch and Services, Chinese Academy of Meteorological Sciences, China Meteorological Administration, Beijing, and Institute of Earth Environment, Chinese Academy of Sciences, Xian, China
3. Air Quality Research Branch, Meteorological Service of Canada, Toronto, Ontario, Canada, and Centre for Atmosphere Watch and Services, Chinese Academy of Meteorological Sciences, China Meteorological Administration, Beijing, China
4. Climate Research Branch, Meteorological Service of Canada, Toronto, Ontario, Canada
5. Air Quality Research Branch, Meteorological Service of Canada, Toronto, Ontario, Canada, and Environment Division, Atmospheric Research and Environment Program, World Meteorological Organization, Geneva, Switzerland
6. Atmospheric Science Programme/Geography, University of British Columbia, Vancouver, British Columbia, Canada
7. Department of Atmospheric Science, School of Physics, Peking University, Beijing, China