1. University of Helsinki, Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland;
2. Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland;
3. University of Kuopio, Department of Applied Physics, P.O. Box 1627, FI-70211 Kuopio, Finland;
4. Helsinki Institute of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland;
5. University of Helsinki, Department of Forest Ecology, P.O. Box 27, FI-00014 University of Helsinki, Finland;
6. University of Copenhagen, Department of Chemistry, Universitetsparken 5, DK-2100 Copenhagen, Denmark;
7. University of Lund, Department of Physical Geography and Ecosystem Analysis, Sölvegatan 12, SE-223 62, Lund, Sweden;
8. Technical University of Crete, Department of Environmental Engineering, Chania, Greece;
9. Norwegian Institute for Air Research, Department of Regional and Global Pollution Issues, P.O. Box 100, NO-2027 Kjeller, Norway;
10. Stockholm University, Department of Applied Environmental Science, Frescativägen 50, SE-10691 Stockholm, Sweden;
11. Risoe-Technical University of Denmark, Department of Wind Energy, Frederiksborgvej 399, P.O. 49, DK-4000 Roskilde, Denmark;
12. Indiana University, Department of Geography, Student Building 120, 701 E. Kirkwood Avenue, Bloomington, IN 47405–7100, USA;
13. Institute of Physics, University of Tartu, 18 Ülikooli St., 50090 Tartu, Estonia;
14. Fakultät für Physik, Universität Wien, Boltzmanngasse 5, A-1090 Wien, Austria;
15. Div. of Nuclear Physics, Lund University, P.O. Box 118, SE-22100 Lund, Sweden;
16. University of Helsinki, Department of Chemistry, P.O. Box 55, FI-00014 University of Helsinki, Finland;
17. Stockholm University, Department of Meteorology (MISU), SE-10691 Stockholm, Sweden;
18. University of Oslo, Department of Geosciences, P.O. Box 1022 Blindern, NO-0315 Oslo, Norway;
19. Norwegian Meteorological Institute, P.O. Box 43 Blindern, NO-0313 Oslo, Norway;
20. Centre for International Climate and Environmental Research (CICERO), Oslo, Norway