1. Department of Chemistry, University of Eastern Finland, P.O. Box 111, Joensuu FI-80101, Finland
2. Aerosol Physics Laboratory, Physics Unit, Tampere University, P.O. Box 692, Tampere FI-33101, Finland
3. Institute of Chemistry, St. Petersburg State University, St. Petersburg 198504, Russian Federation
4. Department of Chemical Engineering, Imperial College London, London SW7 2AZ, U.K.