1. Department of Physics, University of Helsinki, P.O. Box 64, Helsinki, 00014, Finland
2. Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki, 00014, Finland
3. Department of Atmospheric Sciences, University of Washington, Seattle, Washington 98195, United States
4. Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark
5. Institute for Energy and Climate Research (IEK-8), Forschungszentrum Jülich, 52425 Jülich, Germany
6. Aerodyne Research Inc., 45 Manning Road, Billerica, Massachusetts 01821, United States