ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-4775-2010 Explaining global surface aerosol number concentrations in terms of primary emissions and particle formation Spracklen D. V. 1 Carslaw K. S. 1 Merikanto J. 1 Mann G. W. 1 Reddington C. L. 1 Pickering S. 1 Ogren J. A. 2 Andrews E. 2 Baltensperger U. 3 Weingartner E. 3 Boy M. 4 Kulmala M. 4 Laakso L. 4 Lihavainen H. 5 Kivekäs N. 5 Komppula M. 5 20 Mihalopoulos N. 6 Kouvarakis G. 6 Jennings S. G. 7 O'Dowd C. 7 Birmili W. 8 Wiedensohler A. 8 Weller R. 9 Gras J. 10 Laj P. 11 Sellegri K. 12 Bonn B. 13 Krejci R. 14 Laaksonen A. 5 15 Hamed A. 15 Minikin A. 16 Harrison R. M. 17 Talbot R. 18 Sun J. 19 Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, LS2 9JT, UK NOAA/ESRL Global Monitoring Division, 325 Broadway R/GMD1, Boulder, Co 80305, USA Paul Scherrer Institut, Laboratory of Atmospheric Chemistry, 5232 Villigen, Switzerland Department of Physics, University of Helsinki, 00014 Helsinki, Finland Climate Change, Finnish Meteorological Institute, P.O. Box 503, 00101, Helsinki, Finland Department of Chemistry, University of Crete, University campus, P.O. Box 2208, 71003, Voutes, Heraklion, Crete, Greece Department of Physics, National University of Ireland, Galway, Ireland Leibniz Institute for Tropospheric Research, Permoserstrasse 15, 04318 Leipzig, Germany Alfred Wegener Institute, Am Handelshafen 12, 27570 Bremerhaven, Germany CSIRO Marine and Atmospheric Research, Ctr Australian Weather and Climate Res, Aspendale, Victoria, Australia Laboratoire de Glaciologie et Géophysique de l'Environnement CNRS/Université Grenoble 1, Grenoble, France Laboratoire de Météorologie Physique, Université Clermont-Ferrand/ CNRS, Clermont-Ferrand, France Institute for Atmospheric and Environmental Sciences, J. W. Goethe University, Frankfurt/Main, Germany Department of Applied Environmental Science (ITM), Stockholm University, 106 91 Stockholm, Sweeden Department of Physics and Mathematics, University of Eastern Finland, (Kuopio campus), P.O. Box 70211 Kuopio, Finland Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut f�r Physik der Atmosphäre, Oberpfaffenhofen, Germany National Centre for Atmospheric Science, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Climate Change Research Center, University of New Hampshire, Durham, NH 03824 USA Key Laboratory for Atmospheric Chemistry of CMA, Center for Atmosphere Watch and Services, Chinese Academy of Meteorological Sciences, CMA, Beijing 100081, China Kuopio Unit, Finnish Meteorological Institute, Kuopio, Finland 26 05 2010 10 10 4775 4793 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/10/4775/2010/acp-10-4775-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/4775/2010/acp-10-4775-2010.pdf

We synthesised observations of total particle number (CN) concentration from 36 sites around the world. We found that annual mean CN concentrations are typically 300–2000 cm<sup>−3</sup> in the marine boundary layer and free troposphere (FT) and 1000–10 000 cm<sup>−3</sup> in the continental boundary layer (BL). Many sites exhibit pronounced seasonality with summer time concentrations a factor of 2–10 greater than wintertime concentrations. We used these CN observations to evaluate primary and secondary sources of particle number in a global aerosol microphysics model. We found that emissions of primary particles can reasonably reproduce the spatial pattern of observed CN concentration (<i>R</i><sup>2</sup>=0.46) but fail to explain the observed seasonal cycle (<i>R</i><sup>2</sup>=0.1). The modeled CN concentration in the FT was biased low (normalised mean bias, NMB=&minus;88%) unless a secondary source of particles was included, for example from binary homogeneous nucleation of sulfuric acid and water (NMB=&minus;25%). Simulated CN concentrations in the continental BL were also biased low (NMB=&minus;74%) unless the number emission of anthropogenic primary particles was increased or a mechanism that results in particle formation in the BL was included. We ran a number of simulations where we included an empirical BL nucleation mechanism either using the activation-type mechanism (nucleation rate, <i>J</i>, proportional to gas-phase sulfuric acid concentration to the power one) or kinetic-type mechanism (<i>J</i> proportional to sulfuric acid to the power two) with a range of nucleation coefficients. We found that the seasonal CN cycle observed at continental BL sites was better simulated by BL particle formation (<i>R</i><sup>2</sup>=0.3) than by increasing the number emission from primary anthropogenic sources (<i>R</i><sup>2</sup>=0.18). The nucleation constants that resulted in best overall match between model and observed CN concentrations were consistent with values derived in previous studies from detailed case studies at individual sites. In our model, kinetic and activation-type nucleation parameterizations gave similar agreement with observed monthly mean CN concentrations.

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