1. Particle Technology Laboratory, Institute of Process Engineering, Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology (ETH) Zurich, CH-8092 Zurich, Switzerland
2. VTT Technical Research Centre of Finland, Fine Particles, P.O. Box 1000, FI-02044 Espoo and Department of Environmental Science, Fine Particle and Aerosol Technology Laboratory, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland