Articles | Volume 16, issue 3
Atmos. Chem. Phys., 16, 1693–1712, 2016

Special issue: BACCHUS – Impact of Biogenic versus Anthropogenic emissions...

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

Atmos. Chem. Phys., 16, 1693–1712, 2016

Research article 12 Feb 2016

Research article | 12 Feb 2016

Aqueous phase oxidation of sulphur dioxide by ozone in cloud droplets

C. R. Hoyle1,2, C. Fuchs1, E. Järvinen3, H. Saathoff3, A. Dias4, I. El Haddad1, M. Gysel1, S. C. Coburn5, J. Tröstl1, A.-K. Bernhammer6,16, F. Bianchi1, M. Breitenlechner6, J. C. Corbin1, J. Craven7,a, N. M. Donahue8, J. Duplissy9, S. Ehrhart4, C. Frege1, H. Gordon4, N. Höppel3, M. Heinritzi10, T. B. Kristensen11, U. Molteni1, L. Nichman12, T. Pinterich13, A. S. H. Prévôt1, M. Simon10, J. G. Slowik1, G. Steiner9,6,13, A. Tomé14, A. L. Vogel4, R. Volkamer5, A. C. Wagner10, R. Wagner9, A. S. Wexler15, C. Williamson10,b,c, P. M. Winkler13, C. Yan9, A. Amorim14, J. Dommen1, J. Curtius10, M. W. Gallagher12,18, R. C. Flagan7, A. Hansel6,16, J. Kirkby4,10, M. Kulmala9, O. Möhler3, F. Stratmann11, D. R. Worsnop9,17, and U. Baltensperger1 C. R. Hoyle et al.
  • 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
  • 2WSL Institute for Snow and Avalanche Research SLF Davos, Switzerland
  • 3Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, P.O. Box 3640, 76021 Karlsruhe, Germany
  • 4CERN, 1211 Geneva, Switzerland
  • 5Department of Chemistry and Biochemistry & CIRES, University of Colorado, Boulder, CO, USA
  • 6University of Innsbruck, Institute for Ion Physics and Applied Physics, Technikerstrasse 25, 6020 Innsbruck, Austria
  • 7California Institute of Technology, Department of Chemical Engineering, Pasadena, CA 91125, USA
  • 8Carnegie Mellon University Center for Atmospheric Particle Studies, 5000 Forbes Ave, Pittsburgh, PA 15213, USA
  • 9Division of Atmospheric Sciences, Department of Physics, P.O. Box 64, 00014, University of Helsinki, Helsinki, Finland
  • 10Goethe University of Frankfurt, Institute for Atmospheric and Environmental Sciences, 60438 Frankfurt am Main, Germany
  • 11Leibniz Institute for Tropospheric Research, Permoserstrasse 15, 04318 Leipzig, Germany
  • 12School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
  • 13University of Vienna, Faculty of Physics, Aerosol and Environmental Physics, Boltzmanngasse 5, 1090 Vienna, Austria
  • 14CENTRA-SIM, University of Lisbon and University of Beira Interior, 1749-016 Lisbon, Portugal
  • 15Departments of Mechanical and Aeronautical Engineering, Civil and Environmental Engineering, and Land, Air, and Water Resources, University of California, Davis, CA, USA
  • 16Ionicon Analytik GmbH, Eduard-Bodem-Gasse 3, 6020 Innsbruck, Austria
  • 17Aerodyne Research Inc., Billerica, MA 01821, USA
  • 18NERC Instrument PI, National Centre for Atmospheric Science (NCAS), Leeds, UK
  • anow at: Portland Technology Development Division of Intel, Hillsboro, OR, USA
  • bnow at: Chemical Sciences Division NOAA Earth System Research Laboratory 325 Broadway R/CSD2 Boulder, CO, USA
  • cnow at: Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA

Abstract. The growth of aerosol due to the aqueous phase oxidation of sulfur dioxide by ozone was measured in laboratory-generated clouds created in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). Experiments were performed at 10 and −10 °C, on acidic (sulfuric acid) and on partially to fully neutralised (ammonium sulfate) seed aerosol. Clouds were generated by performing an adiabatic expansion – pressurising the chamber to 220 hPa above atmospheric pressure, and then rapidly releasing the excess pressure, resulting in a cooling, condensation of water on the aerosol and a cloud lifetime of approximately 6 min. A model was developed to compare the observed aerosol growth with that predicted using oxidation rate constants previously measured in bulk solutions. The model captured the measured aerosol growth very well for experiments performed at 10 and −10 °C, indicating that, in contrast to some previous studies, the oxidation rates of SO2 in a dispersed aqueous system can be well represented by using accepted rate constants, based on bulk measurements. To the best of our knowledge, these are the first laboratory-based measurements of aqueous phase oxidation in a dispersed, super-cooled population of droplets. The measurements are therefore important in confirming that the extrapolation of currently accepted reaction rate constants to temperatures below 0 °C is correct.

Short summary
A significant portion of sulphate, an important constituent of atmospheric aerosols, is formed via the aqueous phase oxidation of sulphur dioxide by ozone. The rate of this reaction has previously only been measured over a relatively small temperature range. Here, we use the state of the art CLOUD chamber at CERN to perform the first measurements of this reaction rate in super-cooled droplets, confirming that the existing extrapolation of the reaction rate to sub-zero temperatures is accurate.
Final-revised paper