1. a Key Lab of Aerosol, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences , Xi'an , China
2. b Department of Environmental Sciences and Engineering , Xi'an Jiaotong University , Xi'an , China
3. c Division of Atmospheric Sciences , Desert Research Institute , Reno , Nevada , USA
4. d The Hong Kong Polytechnic University , Hong Kong
5. e National Center for Atmospheric Research , Boulder , Colorado , USA