Articles | Volume 17, issue 24
Atmos. Chem. Phys., 17, 15181–15197, 2017

Special issue: The CERN CLOUD experiment (ACP/AMT inter-journal SI)

Atmos. Chem. Phys., 17, 15181–15197, 2017

Research article 21 Dec 2017

Research article | 21 Dec 2017

The role of ions in new particle formation in the CLOUD chamber

Robert Wagner1, Chao Yan1, Katrianne Lehtipalo1,2, Jonathan Duplissy3, Tuomo Nieminen4, Juha Kangasluoma1, Lauri R. Ahonen1, Lubna Dada1, Jenni Kontkanen1,5, Hanna E. Manninen1,6, Antonio Dias6,7, Antonio Amorim7,8, Paulus S. Bauer9, Anton Bergen10, Anne-Kathrin Bernhammer11, Federico Bianchi1, Sophia Brilke9,10, Stephany Buenrostro Mazon1, Xuemeng Chen1, Danielle C. Draper12, Lukas Fischer11, Carla Frege2, Claudia Fuchs2, Olga Garmash1, Hamish Gordon6,13, Jani Hakala1, Liine Heikkinen1, Martin Heinritzi10, Victoria Hofbauer14, Christopher R. Hoyle2, Jasper Kirkby6,10, Andreas Kürten10, Alexander N. Kvashnin15, Tiia Laurila1, Michael J. Lawler12, Huajun Mai16, Vladimir Makhmutov15,17, Roy L. Mauldin III1,18, Ugo Molteni2, Leonid Nichman19,20,21, Wei Nie1,22, Andrea Ojdanic9, Antti Onnela6, Felix Piel10,23, Lauriane L. J. Quéléver1, Matti P. Rissanen1, Nina Sarnela1, Simon Schallhart1, Kamalika Sengupta13, Mario Simon10, Dominik Stolzenburg9, Yuri Stozhkov15, Jasmin Tröstl2, Yrjö Viisanen24, Alexander L. Vogel2,6, Andrea C. Wagner10, Mao Xiao2, Penglin Ye14,20, Urs Baltensperger2, Joachim Curtius10, Neil M. Donahue14, Richard C. Flagan16, Martin Gallagher19, Armin Hansel11,23, James N. Smith4,12, António Tomé7, Paul M. Winkler9, Douglas Worsnop1,3,20,25, Mikael Ehn1, Mikko Sipilä1, Veli-Matti Kerminen1, Tuukka Petäjä1, and Markku Kulmala1 Robert Wagner et al.
  • 1Department of Physics, University of Helsinki, Helsinki, Finland
  • 2Paul Scherrer Institute, Laboratory of Atmospheric Chemistry, Villigen, Switzerland
  • 3Helsinki Institute of Physics, University of Helsinki, P.O. Box 64, Helsinki, Finland
  • 4University of Eastern Finland, Department of Applied Physics, P.O. Box 1627, Kuopio, Finland
  • 5Department of Environmental Science and Analytical Chemistry (ACES) & Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 6CERN, Geneva, Switzerland
  • 7CENTRA – SIM, University of Lisbon and University of Beira Interior, Lisbon, Portugal
  • 8Faculty of Science and Technology, New University of Lisbon, Lisbon, Portugal
  • 9University of Vienna, Faculty of Physics, Vienna, Austria
  • 10Goethe University Frankfurt, Institute for Atmospheric and Environmental Sciences, Frankfurt am Main, Germany
  • 11Institute for Ion and Applied Physics, University of Innsbruck, Innsbruck, Austria
  • 12Department of Chemistry, University of California, Irvine, CA, USA
  • 13University of Leeds, School of Earth and Environment, Leeds, UK
  • 14Center for Atmospheric Particle Studies, Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, PA, USA
  • 15Lebedev Physical Institute, Russian Academy of Sciences, Moscow, Russia
  • 16California Institute of Technology, Pasadena, CA, USA
  • 17Moscow Institute of Physics and Technology (State University), Moscow, Russia
  • 18Department of Atmospheric and Oceanic Sciences, Boulder, Colorado
  • 19School of Earth and Environmental Sciences, University of Manchester, Manchester, UK
  • 20Aerodyne Research Inc., Billerica, MA, USA
  • 21Department of Chemistry, Boston College, Chestnut Hill, MA, USA
  • 22Joint International Research Laboratory of Atmospheric and Earth System Sciences, Nanjing University, Nanjing, China
  • 23IONICON Analytik GmbH, Innsbruck, Austria
  • 24Finnish Meteorological Institute (FMI), P.O. Box 503, Helsinki, Finland
  • 25TOFWERK AG, Uttigenstrasse 22, Thun, Switzerland

Abstract. The formation of secondary particles in the atmosphere accounts for more than half of global cloud condensation nuclei. Experiments at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined the importance of ions for new particle formation, but quantifying their effect in the atmosphere remains challenging. By using a novel instrument setup consisting of two nanoparticle counters, one of them equipped with an ion filter, we were able to further investigate the ion-related mechanisms of new particle formation. In autumn 2015, we carried out experiments at CLOUD on four systems of different chemical compositions involving monoterpenes, sulfuric acid, nitrogen oxides, and ammonia. We measured the influence of ions on the nucleation rates under precisely controlled and atmospherically relevant conditions. Our results indicate that ions enhance the nucleation process when the charge is necessary to stabilize newly formed clusters, i.e., in conditions in which neutral clusters are unstable. For charged clusters that were formed by ion-induced nucleation, we were able to measure, for the first time, their progressive neutralization due to recombination with oppositely charged ions. A large fraction of the clusters carried a charge at 1.5 nm diameter. However, depending on particle growth rates and ion concentrations, charged clusters were largely neutralized by ion–ion recombination before they grew to 2.5 nm. At this size, more than 90 % of particles were neutral. In other words, particles may originate from ion-induced nucleation, although they are neutral upon detection at diameters larger than 2.5 nm. Observations at Hyytiälä, Finland, showed lower ion concentrations and a lower contribution of ion-induced nucleation than measured at CLOUD under similar conditions. Although this can be partly explained by the observation that ion-induced fractions decrease towards lower ion concentrations, further investigations are needed to resolve the origin of the discrepancy.

Final-revised paper