Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 5 2009 10.5194/acpd-9-18235-2009 http://www.atmos-chem-phys-discuss.net/9/18235/2009/ http://www.atmos-chem-phys-discuss.net/9/18235/2009/acpd-9-18235-2009.html http://www.atmos-chem-phys-discuss.net/9/18235/2009/acpd-9-18235-2009.pdf 18235 18270 2009-09-02 Results from the CERN pilot CLOUD experiment J. Duplissy M. B. Enghoff K. L. Aplin F. Arnold H. Aufmhoff M. Avngaard U. Baltensperger T. Bondo R. Bingham K. Carslaw J. Curtius A. David B. Fastrup S. Gagné F. Hahn R. G. Harrison B. Kellett J. Kirkby M. Kulmala L. Laakso A. Laaksonen E. Lillestol M. Lockwood J. Mäkelä V. Makhmutov N. D. Marsh T. Nieminen A. Onnela E. Pedersen J. O. P. Pedersen J. Polny U. Reichl J. H. Seinfeld M. Sipilä Y. Stozhkov F. Stratmann H. Svensmark J. Svensmark R. Veenhof Y. Viisanen P. E. Wagner G. Wehrle E. Weingartner H. Wex M. Wilhelmsson P. M. Winkler CERN, Geneva, Switzerland DTU Space, National Space Institute, Center for Sun-Climate Research, Copenhagen, Denmark Rutherford Appleton Laboratory, Space Science & Technology Department, Chilton, UK Max-Planck Institute for Nuclear Physics, Heidelberg, Germany Paul Scherrer Institut, Laboratory of Atmospheric Chemistry, Villigen, Switzerland University of Leeds, School of Earth and Environment, Leeds, UK Goethe-University of Frankfurt, Institute for Atmospheric and Environmental Sciences, Frankfurt am Main, Germany University of Aarhus, Institute of Physics and Astronomy, Aarhus, Denmark Helsinki Institute of Physics and University of Helsinki, Department of Physics, Helsinki, Finland University of Reading, Department of Meteorology, Reading, UK University of Kuopio, Department of Physics, Kuopio, Finland University of Bergen, Institute of Physics, Bergen, Norway Tampere University of Technology, Department of Physics, Tampere, Finland Lebedev Physical Institute, Solar and Cosmic Ray Research Laboratory, Moscow, Russia California Institute of Technology, Division of Chemistry and Chemical Engineering, Pasadena, USA Leibniz Institute for Tropospheric Research, Leipzig, Germany Finnish Meteorological Institute, Helsinki, Finland University of Vienna, Institute for Experimental Physics, Vienna, Austria During a 4-week run in October–November 2006, a pilot experiment was performed at the CERN Proton Synchrotron in preparation for the CLOUD¹ 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^&minus;3s^&minus;1, and growth rates between 2 and 37 nm h^&minus;1. The corresponding H₂SO₄ concentrations were typically around 10⁶ cm^&minus;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. 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