[1] Div. of Nuclear Physics, Dept. of Physics, Lund University, P.O. Box 118, S-22100 Lund, Sweden
[2] Div. of Ergonomics and Aerosol Technology, Lund University, P.O. Box 118, S-22100 Lund, Sweden
[3] Dept. of Atmospheric Environment, National Environmental Research Institute, P.O. Box 358, DK-4000 Roskilde, Denmark