ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-10829-2010 Atmospheric nucleation: highlights of the EUCAARI project and future directions Kerminen V.-M. 1 2 Petäjä T. 1 Manninen H. E. 1 Paasonen P. 1 Nieminen T. 1 Sipilä M. 1 Junninen H. 1 Ehn M. 1 Gagné S. 1 Laakso L. 1 12 Riipinen I. 1 13 Vehkamäki H. 1 Kurten T. 1 Ortega I. K. 1 Dal Maso M. 1 6 Brus D. 2 Hyvärinen A. 2 Lihavainen H. 2 Leppä J. 2 Lehtinen K. E. J. 2 11 Mirme A. 3 Mirme S. 3 Hõrrak U. 3 Berndt T. 4 Stratmann F. 4 Birmili W. 4 Wiedensohler A. 4 Metzger A. 5 14 Dommen J. 5 Baltensperger U. 5 Kiendler-Scharr A. 6 Mentel T. F. 6 Wildt J. 6 Winkler P. M. 7 15 Wagner P. E. 7 Petzold A. 8 Minikin A. 8 Plass-Dülmer C. 9 Pöschl U. 10 Laaksonen A. 1 11 Kulmala M. 1 Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland Finnish Meteorological Institute, Research and Development, P.O. Box 503, 00101 Helsinki, Finland Institute of Physics, University of Tartu, Ülikooli 18, 50090, Tartu, Estonia Leibniz-nstitute für Troposphärenforschung, Permoserstrasse 15, Leipzig 04318, Germany Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland Institut für Chemie und Dynamik der Geosphäre (ICG), Forschungszentrum Jülich, 52425 Jülich, Germany Fakultät für Physik, Universität Wien, Boltzmanngasse 5, 1090 Wien, Austria Deutsches Zentrum für Luft- und Raumfarhr, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany Hohenpeissenberg Meteorological Observatory, Deutscher Wetterdienst, Germany Max Planck Institute for Chemistry, Biogeochemistry Department, P.O. Box 3060, 55128 Mainz, Germany Department of Physics and Mathematics, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland School of Physical and Chemical Sciences, North-West University, Potchefstroom, South Africa Department of Chemical Engineering, Carnegie Mellon University, 15213, Pittsburgh, PA, USA now at: Ionicon Analytik GmbH, 6020 Innsbruck, Austria now at: Atmospheric Chemistry Division, National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO-80305, USA 18 11 2010 10 22 10829 10848 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/10829/2010/acp-10-10829-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/10829/2010/acp-10-10829-2010.pdf

Within the project EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions), atmospheric nucleation was studied by (i) developing and testing new air ion and cluster spectrometers, (ii) conducting homogeneous nucleation experiments for sulphate and organic systems in the laboratory, (iii) investigating atmospheric nucleation mechanism under field conditions, and (iv) applying new theoretical and modelling tools for data interpretation and development of parameterisations. The current paper provides a synthesis of the obtained results and identifies the remaining major knowledge gaps related to atmospheric nucleation. The most important technical achievement of the project was the development of new instruments for measuring sub-3 nm particle populations, along with the extensive application of these instruments in both the laboratory and the field. All the results obtained during EUCAARI indicate that sulphuric acid plays a central role in atmospheric nucleation. However, also vapours other than sulphuric acid are needed to explain the nucleation and the subsequent growth processes, at least in continental boundary layers. Candidate vapours in this respect are some organic compounds, ammonia, and especially amines. Both our field and laboratory data demonstrate that the nucleation rate scales to the first or second power of the nucleating vapour concentration(s). This agrees with the few earlier field observations, but is in stark contrast with classical thermodynamic nucleation theories. The average formation rates of 2-nm particles were found to vary by almost two orders of magnitude between the different EUCAARI sites, whereas the formation rates of charged 2-nm particles varied very little between the sites. Overall, our observations are indicative of frequent, yet moderate, ion-induced nucleation usually outweighed by much stronger neutral nucleation events in the continental lower troposphere. The most concrete outcome of the EUCAARI nucleation studies are the new semi-empirical nucleation rate parameterizations based on field observations, along with updated aerosol formation parameterizations.

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