1. Leibniz-Institut für Troposphärenforschung e.V., Leipzig 04318, Germany.
2. Department of Physics, 00014 University of Helsinki, Finland.
3. Helsinki Institute of Physics, 00014 University of Helsinki, Finland.
4. Laboratory of Aerosol Chemistry and Physics, Institute of Chemical Process Fundamentals Academy of Sciences of the Czech Republic, Prague 18502, Czech Republic.
5. Finnish Meteorological Institute, Helsinki 00101, Finland.
6. National Center for Atmospheric Research, Boulder, CO 80307, USA.
7. Department of Applied Environmental Science, Stockholm University, Stockholm 10691, Sweden.