Published December 21, 2017 | Version v1
Journal article Open

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

Authors/Creators

  • 1. Department of Physics, University of Helsinki, Helsinki, Finland
  • 2. Paul Scherrer Institute, Laboratory of Atmospheric Chemistry, Villigen, Switzerland
  • 3. Helsinki Institute of Physics, University of Helsinki, P.O. Box 64, Helsinki, Finland
  • 4. University of Eastern Finland, Department of Applied Physics, P.O. Box 1627, Kuopio, Finland
  • 5. Department of Environmental Science and Analytical Chemistry (ACES) & Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 6. CERN, Geneva, Switzerland
  • 7. CENTRA – SIM, University of Lisbon and University of Beira Interior, Lisbon, Portugal
  • 8. Faculty of Science and Technology, New University of Lisbon, Lisbon, Portugal
  • 9. University of Vienna, Faculty of Physics, Vienna, Austria
  • 10. Goethe University Frankfurt, Institute for Atmospheric and Environmental Sciences, Frankfurt am Main, Germany
  • 11. Institute for Ion and Applied Physics, University of Innsbruck, Innsbruck, Austria
  • 12. Department of Chemistry, University of California, Irvine, CA, USA
  • 13. University of Leeds, School of Earth and Environment, Leeds, UK
  • 14. Center for Atmospheric Particle Studies, Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, PA, USA
  • 15. Lebedev Physical Institute, Russian Academy of Sciences, Moscow, Russia
  • 16. California Institute of Technology, Pasadena, CA, USA
  • 17. Moscow Institute of Physics and Technology (State University), Moscow, Russia
  • 18. Department of Atmospheric and Oceanic Sciences, Boulder, Colorado
  • 19. School of Earth and Environmental Sciences, University of Manchester, Manchester, UK
  • 20. Aerodyne Research Inc., Billerica, MA, USA
  • 21. Department of Chemistry, Boston College, Chestnut Hill, MA, USA
  • 22. Joint International Research Laboratory of Atmospheric and Earth System Sciences, Nanjing University, Nanjing, China
  • 23. IONICON Analytik GmbH, Innsbruck, Austria
  • 24. Finnish Meteorological Institute (FMI), P.O. Box 503, Helsinki, Finland
  • 25. TOFWERK AG, Uttigenstrasse 22, Thun, Switzerland

Description

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.

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Additional details

Funding

European Commission
NANODYNAMITE - Quantifying Aerosol Nanoparticle Dynamics by High Time Resolution Experiments 616075
European Commission
QAPPA - Quantifying the atmospheric implications of the solid phase and phase transitions of secondary organic aerosols 335478
European Commission
MOCAPAF - Role of Molecular Clusters in Atmospheric Particle Formation 257360
European Commission
nanoCAVa - Formation of nano-scale clusters from atmospheric vapors 656994
European Commission
CLOUD-TRAIN - CLOUD Initial Training Network (CLOUD TRAIN) 316662
European Commission
CERN-COFUND-2012 - COFUNDing of the CERN Fellowship Programme 2012 600377
European Commission
COALA - Comprehensive molecular characterization of secondary organic aerosol formation in the atmosphere 638703
European Commission
ATMNUCLE - Atmospheric nucleation: from molecular to global scale 227463