1. Norwegian Institute for Air Research, P.O. Box 100, NO-2027 Kjeller, Norway
2. Department of Chemistry, University of Oslo, P.O. Box 1033, NO-0315 Oslo, Norway
3. Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, U.K.
4. Guangzhou Institute of Geochemistry, The Chinese Academy of Sciences, Guangzhou 510640, China