Department of Chemistry, University of Copenhagen, Copenhagen, Denmark

now at: Division of Nuclear Physics, University of Lund, Lund, Sweden

Department of Chemistry, University of Copenhagen, Copenhagen, Denmark

School of Earth {&} Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA

School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland

now at: Division of Atmospheric Sciences, Department of Physics, University of Helsinki, Helsinki, Finland

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland

now at: School of Engineering, Institute of Aerosol and Sensor Technology, University of Applied Sciences Northwestern Switzerland, Windisch, Switzerland

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland