University of Helsinki, Department of Physical Sciences, P.O. Box 64, 00014 University of Helsinki, Finland

University of Helsinki, Department of Physical Sciences, P.O. Box 64, 00014 University of Helsinki, Finland

University of Helsinki, Department of Physical Sciences, P.O. Box 64, 00014 University of Helsinki, Finland

Max Planck Institute for Nuclear Physics (MPIK), Atmospheric Physics Division, P.O. Box 103980, 69029 Heidelberg, Germany

University of Helsinki, Department of Physical Sciences, P.O. Box 64, 00014 University of Helsinki, Finland

Leibniz Institute for Tropospheric Research, Permoserstrasse 15, 04318 Leipzig, Germany

Finnish Meteorological Institute, Erik Palmenin Aukio 1, P.O. Box 503, 00101 Helsinki, Finland

Finnish Meteorological Institute, Erik Palmenin Aukio 1, P.O. Box 503, 00101 Helsinki, Finland

Finnish Meteorological Institute, Erik Palmenin Aukio 1, P.O. Box 503, 00101 Helsinki, Finland

University of Kuopio, Department of Applied Physics, P.O. Box 1627, 70211 Kuopio, Finland

Finnish Meteorological Institute, Erik Palmenin Aukio 1, P.O. Box 503, 00101 Helsinki, Finland

Finnish Meteorological Institute and University of Kuopio, Department of Applied Physics, P.O. Box 1627, 70211 Kuopio, Finland