1. Aerosol Physics Laboratory, Physics Unit, Faculty of Engineering and Natural Sciences, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
2. Tampere Microscopy Center, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
3. VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 Espoo, Finland
4. Atmospheric Composition Research, Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland