1. Institute for Atmospheric and Earth System Research / Physics, Faculty of Science, University of Helsinki, Helsinki, Finland
2. VTT Technical Research Centre of Finland, Espoo, Finland
3. Aalto University, Department of Electronics and Nanoengineering, Espoo, Finland
4. Finnish Meteorological Institute, Helsinki, Finland
5. Aalto University, Department of Applied Physics, New Energy Technologies Group, Espoo, Finland