1. Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland.
2. Department of Physics, University of Helsinki, Helsinki, Finland.
3. School of Earth and Environment, University of Leeds, Leeds, UK.
4. Institute for Atmospheric and Environmental Sciences, Goethe University of Frankfurt, Frankfurt am Main, Germany.
5. Laboratory for Systems, Instrumentation, and Modeling in Science and Technology for Space and the Environment (SIM), University of Lisbon and University of Beira Interior, Lisbon, Portugal.
6. Ionicon Analytik GmbH and University of Innsbruck, Institute for Ion and Applied Physics, Innsbruck, Austria.
7. CERN (European Organization for Nuclear Research), Geneva, Switzerland.
8. Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
9. Helsinki Institute of Physics, University of Helsinki, Helsinki, Finland.
10. University of Eastern Finland, Kuopio, Finland.
11. Faculty of Physics, University of Vienna, Vienna, Austria.
12. Solar and Cosmic Ray Research Laboratory, Lebedev Physical Institute, Moscow, Russia.
13. Leibniz Institute for Tropospheric Research, Leipzig, Germany.
14. Finnish Meteorological Institute, Helsinki, Finland.
15. Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
16. Aerodyne Research Incorporated, Billerica, MA 01821, USA.