1. Department of Earth and Environment, Boston University, Boston, MA 02215, USA.
2. Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China.
3. Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA.
4. Department of Earth and Environmental Engineering, Columbia University, New York, NY 10027, USA.
5. NASA Ames Research Center, Moffett Field, CA 94035, USA.