Junji Cao1, Armond Cohen2, James Hansen3, Richard Lester4, Per Peterson5, Hongjie Xu6. 1. Key Lab of Aerosol Chemistry and Physics, SKLLQG, Institute of Earth Environment, Xi'an 710061, China. 2. Clean Air Task Force, Boston, MA 02108, USA. 3. Earth Institute, Columbia University, New York, NY 10025, USA. jimehansen@gmail.com. 4. Massachusetts Institute of Technology, Cambridge, MA 02139, USA. 5. University of California, Berkeley, CA 94720, USA. 6. Shanghai Institute of Applied Physics, Shanghai 21203, China.