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Results from the CERN pilot CLOUD experiment

Duplissy, J. and Enghoff, M. B. and Aplin, K. L. and Arnold, F. and Aufmhoff, H. and Avngaard, M. and Baltensperger, U. and Bondo, T. and Bingham, R. and Carslaw, K. and Curtius, J. and David, A. and Fastrup, B. and Gagné, S. and Hahn, F. and Harrison, R. G. and Kellett, B. and Kirkby, J. and Kulmala, M. and Laakso, L. and Laaksonen, A. and Lillestol, E. and Lockwood, M. and Mäkelä, J. and Makhmutov, V. and Marsh, N. D. and Nieminen, T. and Onnela, A. and Pedersen, E. and Pedersen, J. O. P. and Polny, J. and Reichl, U. and Seinfeld, J. H. and Sipilä, M. and Stozhkov, Y. and Stratmann, F. and Svensmark, H. and Svensmark, J. and Svensmark, R. and Veenhof, B. and Viisanen, Y. and Wagner, P. E. and Wehrle, G. and Weingartner, E. and Wex, H. and Wilhelmsson, M. and Winkler, P. M. (2010) Results from the CERN pilot CLOUD experiment. Atmospheric Chemistry and Physics, 10 (4). pp. 1635-1647. ISSN 1680-7316.

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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 H_2SO_4 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^(−3)s^(−1), and growth rates between 2 and 37 nm h^(−1). The corresponding H_2SO_4 concentrations were typically around 106 cm^(−3) or less. The experimentally-measured formation rates and H_2SO_4 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).

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Seinfeld, J. H.0000-0003-1344-4068
Additional Information:© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 7 August 2009 – Published in Atmos. Chem. Phys. Discuss.: 2 September 2009. Revised: 18 December 2009 – Accepted: 15 January 2010 – Published: 15 February 2010. We would like to thank CERN for its support of the experiment and for the efficient operation of the Proton Synchrotron. We would also like to thank the staff of Pharma Steel, Copenhagen, for their contributions to the design and construction of the aerosol chamber under project DAN 635. J. D. is supported by the European Community under the FP7 Marie Curie Initial Training Network “CLOUD-ITN” (PITN-GA-2008-215072). Edited by: M. Petters.
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Marie Curie FellowshipPITN-GA-2008-215072
European CommunityDAN 635
Issue or Number:4
Record Number:CaltechAUTHORS:20100317-085129359
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17760
Deposited By: Tony Diaz
Deposited On:22 Mar 2010 02:57
Last Modified:03 Oct 2019 01:33

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