Articles | Volume 10, issue 4
Atmos. Chem. Phys., 10, 1635–1647, 2010
Atmos. Chem. Phys., 10, 1635–1647, 2010

  15 Feb 2010

15 Feb 2010

Results from the CERN pilot CLOUD experiment

J. Duplissy1, M. B. Enghoff2, K. L. Aplin3, F. Arnold4, H. Aufmhoff4, M. Avngaard2, U. Baltensperger5, T. Bondo2, R. Bingham3, K. Carslaw6, J. Curtius7, A. David1, B. Fastrup8, S. Gagné9, F. Hahn1, R. G. Harrison10, B. Kellett3, J. Kirkby1, M. Kulmala9, L. Laakso9, A. Laaksonen11, E. Lillestol12, M. Lockwood3, J. Mäkelä13, V. Makhmutov14, N. D. Marsh2, T. Nieminen9, A. Onnela1, E. Pedersen8, J. O. P. Pedersen2, J. Polny2, U. Reichl4, J. H. Seinfeld15, M. Sipilä9, Y. Stozhkov14, F. Stratmann16, H. Svensmark2, J. Svensmark2, R. Veenhof1, B. Verheggen5, Y. Viisanen17, P. E. Wagner18, G. Wehrle5, E. Weingartner5, H. Wex16, M. Wilhelmsson1, and P. M. Winkler18 J. Duplissy et al.
  • 1CERN, PH Department, Geneva, Switzerland
  • 2DTU Space, National Space Institute, Center for Sun-Climate Research, Copenhagen, Denmark
  • 3Rutherford Appleton Laboratory, Space Science & Technology Department, Chilton, UK
  • 4Max-Planck Institute for Nuclear Physics, Heidelberg, Germany
  • 5Paul Scherrer Institut, Laboratory of Atmospheric Chemistry, Villigen, Switzerland
  • 6University of Leeds, School of Earth and Environment, Leeds, UK
  • 7Goethe-University of Frankfurt, Institute for Atmospheric and Environmental Sciences, Frankfurt am Main, Germany
  • 8University of Aarhus, Institute of Physics and Astronomy, Aarhus, Denmark
  • 9Helsinki Institute of Physics and University of Helsinki, Department of Physics, Helsinki, Finland
  • 10University of Reading, Department of Meteorology, Reading, UK
  • 11University of Kuopio, Department of Physics, Kuopio, Finland
  • 12University of Bergen, Institute of Physics, Bergen, Norway
  • 13Tampere University of Technology, Department of Physics, Tampere, Finland
  • 14Lebedev Physical Institute, Solar and Cosmic Ray Research Laboratory, Moscow, Russia
  • 15California Institute of Technology, Division of Chemistry and Chemical Engineering, Pasadena, USA
  • 16Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • 17Finnish Meteorological Institute, Helsinki, Finland
  • 18University of Vienna, Institute for Experimental Physics, Vienna, Austria

Abstract. During a 4-week run in October–November 2006, a pilot experiment was performed at the CERN Proton Synchrotron in preparation for the Cosmics Leaving OUtdoor Droplets (CLOUD) experiment, whose aim is to study the possible influence of cosmic rays on clouds. The purpose of the pilot experiment was firstly to carry out exploratory measurements of the effect of ionising particle radiation on aerosol formation from trace H2SO4 vapour and secondly to provide technical input for the CLOUD design. A total of 44 nucleation bursts were produced and recorded, with formation rates of particles above the 3 nm detection threshold of between 0.1 and 100 cm−3s−1, and growth rates between 2 and 37 nm h−1. The corresponding H2O concentrations were typically around 106 cm−3 or less. The experimentally-measured formation rates and H2SO4 concentrations are comparable to those found in the atmosphere, supporting the idea that sulphuric acid is involved in the nucleation of atmospheric aerosols. However, sulphuric acid alone is not able to explain the observed rapid growth rates, which suggests the presence of additional trace vapours in the aerosol chamber, whose identity is unknown. By analysing the charged fraction, a few of the aerosol bursts appear to have a contribution from ion-induced nucleation and ion-ion recombination to form neutral clusters. Some indications were also found for the accelerator beam timing and intensity to influence the aerosol particle formation rate at the highest experimental SO2 concentrations of 6 ppb, although none was found at lower concentrations. Overall, the exploratory measurements provide suggestive evidence for ion-induced nucleation or ion-ion recombination as sources of aerosol particles. However in order to quantify the conditions under which ion processes become significant, improvements are needed in controlling the experimental variables and in the reproducibility of the experiments. Finally, concerning technical aspects, the most important lessons for the CLOUD design include the stringent requirement of internal cleanliness of the aerosol chamber, as well as maintenance of extremely stable temperatures (variations below 0.1 °C

Final-revised paper