1. Department of Environmental Science and Analytical Chemistry (ACES) and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
2. Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
3. Department of Physics, University of Helsinki, Helsinki, Finland
4. Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
5. Department of Chemistry, University of California, Irvine, California, USA
6. Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
7. Institute for Atmospheric and Climate Science, ETH, Zürich, Switzerland
8. Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA
9. Helsinki Institute of Physics, University of Helsinki, Helsinki, Finland
10. CERN, PH Department, Geneva, Switzerland
11. Institute for Atmospheric and Environmental Sciences, Goethe University of Frankfurt, Frankfurt am Main, Germany
12. Faculty of Physics, University of Vienna, Vienna, Austria
13. Aerodyne Research Inc., Billerica, Massachusetts, USA