Environment Research Institute, Shandong University, Jinan, Shandong 250100, China State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing 100083, China School of Earth and Space Exploration & Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1404, USA Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Kumamoto 862-8502, Japan Centre for Atmospheric Watch and Services, Chinese Academy of Meteorological Sciences, China Meteorological Administration, Beijing, China Weather Modification Office of Shanxi Province, Taiyuan 030032, China