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    Original Research Papers

    Size distribution, mass concentration, chemical and mineralogical composition and derived optical parameters of the boundary layer aerosol at Tinfou, Morocco, during SAMUM 2006

    Authors:

    K. Kandler ,

    Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, DE
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    L. Schütz,

    Institute für Physik der Atmosphäre, Johannes-Gutenberg-Universität, DE
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    C. Deutscher,

    Institute für Physik der Atmosphäre, Johannes-Gutenberg-Universität, DE
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    M. Ebert,

    Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, DE
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    H. Hofmann,

    Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, DE
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    S. Jäckel,

    Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, DE
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    R. Jaenicke,

    Institute für Physik der Atmosphäre, Johannes-Gutenberg-Universität, DE
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    P. Knippertz,

    Institute für Physik der Atmosphäre, Johannes-Gutenberg-Universität, DE
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    K. Lieke,

    Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, DE
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    A. Massling,

    Leibniz-Institut für Troposphärenforschung, DE
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    A. Petzold,

    Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), DE
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    A. Schladitz,

    Leibniz-Institut für Troposphärenforschung, DE
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    B. Weinzierl,

    Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), DE
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    A. Wiedensohler,

    Leibniz-Institut für Troposphärenforschung, DE
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    S. Zorn,

    Institute für Physik der Atmosphäre, Johannes-Gutenberg-Universität, DE
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    S. Weinbruch

    Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, DE
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    Abstract

    During the SAMUM 2006 field campaign in southern Morocco, physical and chemical properties of desert aerosols were measured. Mass concentrations ranging from 30μgm−3 for PM2.5 under desert background conditions up to 300 000μgm−3 for total suspended particles (TSP) during moderate dust storms were measured. TSP dust concentrations are correlated with the local wind speed, whereasPM10 andPM2.5 concentrations are determined by advection from distant sources. Size distributions were measured for particles with diameter between 20 nm and 500μm (parametrizations are given). Two major regimes of the size spectrum can be distinguished. For particles smaller than 500 nm diameter, the distributions show maxima around 80 nm, widely unaffected of varying meteorological and dust emission conditions. For particles larger than 500 nm, the range of variation may be up to one order of magnitude and up to three orders of magnitude for particles larger than 10μm. The mineralogical composition of aerosol bulk samples was measured by X-ray powder diffraction. Major constituents of the aerosol are quartz, potassium feldspar, plagioclase, calcite, hematite and the clay minerals illite, kaolinite and chlorite. A small temporal variability of the bulk mineralogical composition was encountered. The chemical composition of approximately 74 000 particles was determined by electron microscopic single particle analysis. Three size regimes are identified: for smaller than 500 nm in diameter, the aerosol consists of sulphates and mineral dust. For larger than 500 nm up to 50μm, mineral dust dominates, consisting mainly of silicates, and—to a lesser extent—carbonates and quartz. For diameters larger than 50μm, approximately half of the particles consist of quartz. Time series of the elemental composition show a moderate temporal variability of the major compounds. Calcium-dominated particles are enhanced during advection from a prominent dust source in Northern Africa (Chott El Djerid and surroundings). The particle aspect ratio was measured for all analysed particles. Its size dependence reflects that of the chemical composition. For larger than 500 nm particle diameter, a median aspect ratio of 1.6 is measured. Towards smaller particles, it decreases to about 1.3 (parametrizations are given). From the chemical/mineralogical composition, the aerosol complex refractive index was determined for several wavelengths from ultraviolet to near-infrared. Both real and imaginary parts show lower values for particles smaller than 500 nm in diameter (1.55–2.8 × 10−3i at 530 nm) and slightly higher values for larger particles (1.57–3.7 × 10−3i at 530 nm).

    How to Cite: Kandler, K., Schütz, L., Deutscher, C., Ebert, M., Hofmann, H., Jäckel, S., Jaenicke, R., Knippertz, P., Lieke, K., Massling, A., Petzold, A., Schladitz, A., Weinzierl, B., Wiedensohler, A., Zorn, S. and Weinbruch, S., 2009. Size distribution, mass concentration, chemical and mineralogical composition and derived optical parameters of the boundary layer aerosol at Tinfou, Morocco, during SAMUM 2006. Tellus B: Chemical and Physical Meteorology, 61(1), pp.32–50. DOI: http://doi.org/10.1111/j.1600-0889.2008.00385.x
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      Published on 01 Jan 2009
    Peer Reviewed
     CC BY 4.0
     Accepted on 28 Jul 2008            Submitted on 28 Dec 2007

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