1. Department for Urban Environment and Industry, Norwegian Institute for Air Research, P.O. Box 100, NO-2027 Kjeller, Norway
2. Department of Atmospheric Environment, National Environment Research Institute, Aarhus University, Frederiksborgvej 399, DK-4000 Roskilde, Denmark
3. Department of Physical Sciences, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
4. Department of Technology, Metropolia University of Applied Sciences, P.O. Box 4000, FI-00180 Helsinki, Finland
5. Department of Meteorology, Stockholm University, Svante Arrhenius väg 16C, S-10691 Stockholm, Sweden