1. School of Earth and Environment; University of Leeds; Leeds UK
2. CERN; Geneva Switzerland
3. Institute for Atmosphere and Environment; Goethe University Frankfurt; Frankfurt Germany
4. Laboratory of Atmospheric Chemistry; Paul Scherrer Institute; Villigen Switzerland
5. Department of Physics, Division of Atmospheric Sciences; University of Helsinki; Helsinki Finland
6. School of Engineering and Applied Sciences, Department of Chemistry and Chemical Biology; Harvard University; Cambridge Massachusetts USA
7. Center for Atmospheric Particle Studies; Carnegie Mellon University; Pittsburgh Pennsylvania USA
8. Finnish Meteorological Institute; Atmospheric Research Centre of Eastern Finland; Kuopio Finland
9. Helsinki Institute of Physics; Helsinki Finland
10. Now at Atmospheric Chemistry Department; Max Planck Institute for Chemistry; Mainz Germany
11. Institute for Ion Physics and Applied Physics, Division of Chemistry and Chemical Engineering; California Institute of Technology; Pasadena California USA
12. University of Innsbruck; Innsbruck Austria
13. SLFWSL Institute for Snow and Avalanche Research; Davos Switzerland
14. Solar and Cosmic Ray Research Laboratory; Lebedev Physical Institute; Moscow Russia
15. Leibniz Institute for Tropospheric Research; Leipzig Germany
16. Cooperative Institute for Research in Environmental Sciences; University of Colorado Boulder and National Oceanic and Atmospheric Administration Earth System Research Laboratory; Boulder Colorado USA
17. Faculty of Physics; University of Vienna; Vienna Austria