1. National Center for Atmospheric Research, Boulder, CO 80307, USA
2. Max Planck Institute for Meteorology, 20146 Hamburg, Germany
3. Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, China
4. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA
5. National Oceanic and Atmospheric Administration, Chemical Sciences Laboratory, Boulder, CO 80305, USA