E. Z. Nordin, A. C. Eriksson , J. E. Carlsson, P. Nilsson, M. K. Kajos, P. Roldin, J. Rissler, E. Swietlicki, B. Svenningsson, M. Bohgard, M. Kulmala, M. Hallquist, J. Pagels 1 Ergonomics and Aerosol Technology, Lund University, P.O. Box 118 SE-221 00 Lund, Sweden Division of Nuclear Physics, Lund University, P.O. Box 118 SE-221 00 Lund, Sweden Department of Physic, University of Helsinki, P.O. Box 64, FIN-00014 University of Helsinki, Finland Department of Chemistry, Atmospheric Science, University of Gothenburg, 412 96 Gothenburg, Sweden