Atmos. Chem. Phys. Discuss., 11, 18249-18318, 2011
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Primary versus secondary contributions to particle number concentrations in the European boundary layer
C. L. Reddington1, K. S. Carslaw1, D. V. Spracklen1, M. G. Frontoso2, L. Collins1, J. Merikanto1,3, A. Minikin4, T. Hamburger4, H. Coe5, M. Kulmala3, P. Aalto3, H. Flentje6, C. Plass-Dülmer6, W. Birmili7, A. Wiedensohler7, B. Wehner7, T. Tuch7, A. Sonntag7, C. D. O'Dowd8, S. G. Jennings8, R. Dupuy8, U. Baltensperger9, E. Weingartner9, H.-C. Hansson10, P. Tunved10, P. Laj11, K. Sellegri12, J. Boulon12, J.-P. Putaud13, C. Gruening13, E. Swietlicki14, P. Roldin14, J. S. Henzing15, M. Moerman15, N. Mihalopoulos16, G. Kouvarakis16, V. Ždímal17, N. Zíková17, A. Marinoni18, P. Bonasoni18, and R. Duchi18
1Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, UK
2C2SM – ETH Zürich, Zürich, Switzerland
3Division of Atmospheric Sciences, Department of Physics, University of Helsinki, Helsinki, Finland
4Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
5School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK
6Deutscher Wetterdienst, Meteorologisches Observatorium Hohenpeißenberg, Germany
7Leibniz Institute for Tropospheric Research, Leipzig, Germany
8School of Physics & Centre for Climate and Air Pollution Studies, Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland
9Paul Scherrer Institut, Laboratory for Atmospheric Chemistry, 5232 Villigen, Switzerland
10Institute for Applied Environmental Research, Stockholm University, Stockholm, Sweden
11UJF-Grenoble 1 / CNRS, LGGE UMR 5183, Grenoble 38041, France
12Laboratoire de Météorologie Physique, CNRS, Université Blaise Pascal, Aubière cedex, France
13European Commission, Joint Research Centre, Institute of Environment and Sustainability, Ispra, Italy
14Division of Nuclear Physics, Lund University, P.O. Box 118, 22100 Lund, Sweden
15Netherlands Organisation for Applied Scientific Research TNO, Utrecht, The Netherlands
16Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, Crete, Greece
17Institute of Chemical Process Fundamentals of the AS CR, Prague, Czech Republic
18CNR- Institute for Atmospheric Sciences and Climate, Bologna, Italy

Abstract. It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. In large-scale models, there is considerable uncertainty associated with treatments of particle formation (nucleation) in the boundary layer (BL) and in the size distribution of emitted primary particles, leading to uncertainties in predicted cloud condensation nuclei (CCN) concentrations. Here we quantify how primary particle emissions and secondary particle formation influence size-resolved particle number concentrations in the BL using a global aerosol microphysics model and observations made during the May 2008 campaign of the European Integrated Project on Aerosol Cloud Climate Air Quality Interactions (EUCAARI). Observations are available from the DLR Falcon 20 aircraft and from 15 ground sites of the European Supersites for Atmospheric Aerosol Research (EUSAAR) and the German Ultrafine Aerosol Network (GUAN). Measurements include total and non-volatile particle number concentrations and the particle size distribution between ~3 nm and ~1 μm. We tested four different parameterisations for BL nucleation and two assumptions for the emission size distribution of anthropogenic and wildfire carbonaceous particles. When we emit small carbonaceous particles (recommended by the Aerosol Intercomparison project, AEROCOM), the spatial distributions of campaign-mean number concentrations >50 nm (N50) and >100 nm (N100) dry diameter were well captured by the model (R2~0.9) and the normalised mean bias (NMB) was also small (−5 % for N50 and 12 % for N100). Emission of larger particles, which we consider to be more realistic for global models, results in equally good correlation but larger bias (R2~0.8, NMB = −51 % and −21 %), which could be partly but not entirely compensated by BL nucleation. The model also predicts the particle concentration frequency distribution fairly well, with an overlap of modelled and observed N50 hourly histograms of ~60 % across all sites. However, the model-observation temporal correlation on an hourly time scale is poor (R2≤0.1) for this period. These comparisons show that caution is required when drawing conclusions about model realism from time or site-averaged data or frequency histograms when deterministic behaviour is not captured at individual sites. From this 1-month intensive European dataset it is not possible to determine a reliable estimate of the fraction of CCN-sized particles from primary and secondary sources, although the size of primary emitted particles is shown to be a major source of uncertainty.

Citation: Reddington, C. L., Carslaw, K. S., Spracklen, D. V., Frontoso, M. G., Collins, L., Merikanto, J., Minikin, A., Hamburger, T., Coe, H., Kulmala, M., Aalto, P., Flentje, H., Plass-Dülmer, C., Birmili, W., Wiedensohler, A., Wehner, B., Tuch, T., Sonntag, A., O'Dowd, C. D., Jennings, S. G., Dupuy, R., Baltensperger, U., Weingartner, E., Hansson, H.-C., Tunved, P., Laj, P., Sellegri, K., Boulon, J., Putaud, J.-P., Gruening, C., Swietlicki, E., Roldin, P., Henzing, J. S., Moerman, M., Mihalopoulos, N., Kouvarakis, G., Ždímal, V., Zíková, N., Marinoni, A., Bonasoni, P., and Duchi, R.: Primary versus secondary contributions to particle number concentrations in the European boundary layer, Atmos. Chem. Phys. Discuss., 11, 18249-18318, doi:10.5194/acpd-11-18249-2011, 2011.
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