1. National Oceanic and Atmospheric Administration Chemical Sciences Laboratory, Boulder, CO 80305, USA.
2. Insititut für Physik der Atmosphäre, DLR Oberpfaffenhofen, Wessling, Germany.
3. National Center for Atmospheric Research, Boulder, CO 80305, USA.
4. Department of Atmospheric and Oceanic Sciences, Laboratory for Atmospheric and Space Sciences, University of Colorado, Boulder, CO 80309, USA.
5. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA.
6. Institute for Environmental and Climate Research, Jinan University, Guangzhou, China.