Atmos. Chem. Phys., 10, 4775–4793, 2010 www.atmos-chem-phys.net/10/4775/2010/ doi:10.5194/acp-10-4775-2010 © Author(s) 2010. CC Attribution 3.0 License. Atmospheric Chemistry and Physics Explaining global surface aerosol number concentrations in terms of primary emissions and particle formation D. V. Spracklen 1 , K. S. Carslaw 1 , J. Merikanto 1 , G. W. Mann 1 , C. L. Reddington 1 , S. Pickering 1 , J. A. Ogren 2 , E. Andrews 2 , U. Baltensperger 3 , E. Weingartner 3 , M. Boy 4 , M. Kulmala 4 , L. Laakso 4 , H. Lihavainen 5 , N. Kivek¨ as 5 , M. Komppula 5,20 , N. Mihalopoulos 6 , G. Kouvarakis 6 , S. G. Jennings 7 , C. O’Dowd 7 , W. Birmili 8 , A. Wiedensohler 8 , R. Weller 9 , J. Gras 10 , P. Laj 11 , K. Sellegri 12 , B. Bonn 13 , R. Krejci 14 , A. Laaksonen 5,15 , A. Hamed 15 , A. Minikin 16 , R. M. Harrison 17 , R. Talbot 18 , and J. Sun 19 1 Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, LS2 9JT, UK 2 NOAA/ESRL Global Monitoring Division, 325 Broadway R/GMD1, Boulder, Co 80305, USA 3 Paul Scherrer Institut, Laboratory of Atmospheric Chemistry, 5232 Villigen, Switzerland 4 Department of Physics, University of Helsinki, 00014 Helsinki, Finland 5 Climate Change, Finnish Meteorological Institute, P.O. Box 503, 00101, Helsinki, Finland 6 Department of Chemistry, University of Crete, University campus, P.O. Box 2208, 71003, Voutes, Heraklion, Crete, Greece 7 Department of Physics, National University of Ireland, Galway, Ireland 8 Leibniz Institute for Tropospheric Research, Permoserstrasse 15, 04318 Leipzig, Germany 9 Alfred Wegener Institute, Am Handelshafen 12, 27570 Bremerhaven, Germany 10 CSIRO Marine and Atmospheric Research, Ctr Australian Weather and Climate Res, Aspendale, Victoria, Australia 11 Laboratoire de Glaciologie et G´ eophysique de l’Environnement CNRS/Universit´ e Grenoble 1, Grenoble, France 12 Laboratoire de M´ et´ eorologie Physique, Universit´ e Clermont-Ferrand/ CNRS, Clermont-Ferrand, France 13 Institute for Atmospheric and Environmental Sciences, J. W. Goethe University, Frankfurt/Main, Germany 14 Department of Applied Environmental Science (ITM), Stockholm University, 106 91 Stockholm, Sweeden 15 Department of Physics and Mathematics, University of Eastern Finland, (Kuopio campus), P.O. Box 70211 Kuopio, Finland 16 Deutsches Zentrum f ¨ ur Luft- und Raumfahrt (DLR), Institut fr Physik der Atmosph¨ are, Oberpfaffenhofen, Germany 17 National Centre for Atmospheric Science, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK 18 Climate Change Research Center, University of New Hampshire, Durham, NH 03824 USA 19 Key Laboratory for Atmospheric Chemistry of CMA, Center for Atmosphere Watch and Services, Chinese Academy of Meteorological Sciences, CMA, Beijing 100081, China 20 Kuopio Unit, Finnish Meteorological Institute, Kuopio, Finland Received: 10 November 2009 – Published in Atmos. Chem. Phys. Discuss.: 10 December 2009 Revised: 3 May 2010 – Accepted: 17 May 2010 – Published: 26 May 2010 Abstract. We synthesised observations of total particle num- ber (CN) concentration from 36 sites around the world. We found that annual mean CN concentrations are typically 300– 2000 cm −3 in the marine boundary layer and free tropo- sphere (FT) and 1000–10 000 cm −3 in the continental bound- ary layer (BL). Many sites exhibit pronounced seasonality with summer time concentrations a factor of 2–10 greater than wintertime concentrations. We used these CN obser- Correspondence to: D. V. Spracklen (dominick@env.leeds.ac.uk) vations 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 (R 2 =0.46) but fail to explain the observed seasonal cycle (R 2 =0.1). The modeled CN concentration in the FT was biased low (nor- malised mean bias, NMB=−88%) unless a secondary source of particles was included, for example from binary homoge- neous nucleation of sulfuric acid and water (NMB=−25%). Simulated CN concentrations in the continental BL were also biased low (NMB=−74%) unless the number emis- sion of anthropogenic primary particles was increased or a Published by Copernicus Publications on behalf of the European Geosciences Union.