1. Key Laboratory of Aerosol Chemistry & Physics, State Key Laboratory of Loess and Quaternary Geology (SKLLQG), Institute of Earth Environment, Chinese Academy of Sciences (CAS), Xi’an 710061, P. R. China
2. CAS Center for Excellence in Quaternary Science and Global Change, Xi’an 710061, P. R. China
3. Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China