Henning Finkenzeller^1,2, Siddharth Iyer³, Theodore Konstantinos Koenig^1,2, Xucheng He³, Dexian Chen⁴, Andreas Kurten⁵, Joschka Pfeiffer⁵, Neil McPherson Donahue⁴, Joachim Curtius⁵, Jasper Kirkby^5,6, Markku Tapio Kulmala^3,7, Mikko Sipilä³, Theo Kurten³, Rainer M Volkamer^1,2 and CLOUD collaboration, (1)University of Colorado at Boulder, Boulder, CO, United States, (2)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (3)University of Helsinki, Helsinki, Finland, (4)Carnegie Mellon University, Pittsburgh, PA, United States, (5)Goethe University Frankfurt, Frankfurt, Germany, (6)CERN European Organization for Nuclear Research, Physics, Geneva, Switzerland, (7)Beijing University of Chemical Technology, Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing, China