ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-2491-2012 Complex refractive indices of Saharan dust samples at visible and near UV wavelengths: a laboratory study Wagner R. 1 Ajtai T. 2 Kandler K. 3 Lieke K. 3 Linke C. 1 Müller T. 4 Schnaiter M. 1 Vragel M. 1 Karlsruhe Inst. of Technology, Inst. for Meteorology and Climate Research, P.O. Box 3640, 76021 Karlsruhe, Germany University of Szeged, Department of Optics and Quantum Electronics, Dóm tér 9, 6720 Szeged, Hungary Darmstadt University of Technology, Institute of Applied Geosciences, Schnittspahnstr. 9, 64287 Darmstadt, Germany Leibniz Institute for Tropospheric Research, Permoserstr. 15, 04318 Leipzig, Germany 05 03 2012 12 5 2491 2512 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/12/2491/2012/acp-12-2491-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/2491/2012/acp-12-2491-2012.pdf

We have retrieved the wavelength-dependent imaginary parts of the complex refractive index for five different Saharan dust aerosol particles of variable mineralogical composition at wavelengths between 305 and 955 nm. The dust particles were generated by dispersing soil samples into a laboratory aerosol chamber, typically yielding particle sizes with mean diameters ranging from 0.3 to 0.4 μm and maximum diameters from 2 to 4 μm. The extinction and absorption coefficients as well as the number size distribution of the dust particles were simultaneously measured by various established techniques. An inversion scheme based on a spheroidal dust model was employed to deduce the refractive indices. The retrieved imaginary parts of the complex refractive index were in the range from 0.003 to 0.005, 0.005 to 0.011, and 0.016 to 0.050 at the wavelengths 955, 505, and 305 nm. The hematite content of the dust particles was determined by electron-microscopical single particle analysis. Hematite volume fractions in the range from 1.1 to 2.7% were found for the different dusts, a range typical for atmospheric mineral dust. We have performed a sensitivity study to assess how accurately the retrieved imaginary refractive indices could be reproduced by calculations with mixing rule approximations using the experimentally determined hematite contents as input.

 References % vor jede Referenz Ajtai, T., Filep, A., Schnaiter, M., Linke, C., Vragel, M., Bozoki, Z., Szabo, G., and Leisner, T.: A novel multi-wavelength photoacoustic spectrometer for the measurement of the UV-vis-NIR spectral absorption coefficient of atmospheric aerosols, J. Aerosol Sci., 41, 1020–1029, 2010. % vor jede Referenz Alfaro, S. C., Lafon, S., Rajot, J. L., Formenti, P., Gaudichet, A., and Maille, M.: Iron oxides and light absorption by pure desert dust: An experimental study, J. Geophys. Res.-Atmos., 109, D08208, http://dx.doi.org/10.1029/2003JD004374doi:10.1029/2003JD004374, 2004. % vor jede Referenz Balkanski, Y., Schulz, M., Claquin, T., and Guibert, S.: Reevaluation of Mineral aerosol radiative forcings suggests a better agreement with satellite and AERONET data, Atmos. Chem. Phys., 7, 81–95, http://dx.doi.org/10.5194/acp-7-81-2007doi:10.5194/acp-7-81-2007, 2007. % vor jede Referenz Baran, A. J. and Havemann, S.: Rapid computation of the optical properties of hexagonal columns using complex angular momentum theory, J. Quant. Spectrosc. Ra., 63, 499–519, 1999. % vor jede Referenz Baran, A. J., Francis, P. N., Havemann, S., and Yang, P.: A study of the absorption and extinction properties of hexagonal ice columns and plates in random and preferred orientation, using exact T-matrix theory and aircraft observations of cirrus, J. Quant. Spectrosc. Ra., 70, 505–518, 2001. % vor jede Referenz Bedidi, A. and Cervelle, B.: Light-Scattering by Spherical-Particles with Hematite and Geothite-Like Optical-Properties – Effect of Water Impregnation, J. Geophys. Res.-Sol. Ea., 98, 11941–11952, 1993. % vor jede Referenz Bohren, C. F. and Huffman, D. R.: Absorption and Scattering of Light by Small Particles, John Wiley & Sons, Inc., New York, 1983. % vor jede Referenz Chung, F. H.: Quantitative Interpretation of X-Ray-Diffraction Patterns of Mixtures. 1. Matrix-Flushing Method for Quantitative Multicomponent Analysis, J. Appl. Crystallogr., 7, 519–525, 1974. % vor jede Referenz Claquin, T., Schulz, M., and Balkanski, Y. J.: Modeling the mineralogy of atmospheric dust sources, J. Geophys. Res.-Atmos., 104, 22243–22256, 1999. % vor jede Referenz Draine, B. T. and Flatau, P. J., Discrete-Dipole Approximation for Scattering Calculations, J. Opt. Soc. Am. A, 11, 1491–1499, 1994. % vor jede Referenz Dubovik, O., Holben, B., Eck, T. F., Smirnov, A., Kaufman, Y. J., King, M. D., Tanre, D., and Slutsker, I., Variability of absorption and optical properties of key aerosol types observed in worldwide locations, J. Atmos. Sci., 59, 590–608, 2002a. % vor jede Referenz Dubovik, O., Holben, B. N., Lapyonok, T., Sinyuk, A., Mishchenko, M. I., Yang, P., and Slutsker, I.: Non-spherical aerosol retrieval method employing light scattering by spheroids, Geophys. Res. Lett., 29, 1415, http://dx.doi.org/10.1029/2001GL014506doi:10.1029/2001GL014506, 2002b. % vor jede Referenz Dubovik, O., Sinyuk, A., Lapyonok, T., Holben, B. N., Mishchenko, M., Yang, P., Eck, T. F., Volten, H., Munoz, O., Veihelmann, B., van der Zande, W. J., Leon, J. F., Sorokin, M., and Slutsker, I.: Application of spheroid models to account for aerosol particle nonsphericity in remote sensing of desert dust, J. Geophys. Res.-Atmos., 111, D11208, http://dx.doi.org/10.1029/2005JD006619doi:10.1029/2005JD006619, 2006. % vor jede Referenz Fournier, G. R. and Evans, B. T. N.: Approximation to Extinction Efficiency for Randomly Oriented Spheroids, Appl. Optics, 30, 2042–2048, 1991. % vor jede Referenz Hansen, J. E. and Travis, L. D.: Light-Scattering in Planetary Atmospheres, Space. Sci. Rev., 16, 527–610, 1974. % vor jede Referenz Hinds, W. C.: Aerosol Technology, John Wiley & Sons, Inc., New York, 1999. % vor jede Referenz ICDD: Powder Diffraction File PDF-2, JCPDS – International Center for Diffraction Data, Newton Square, PA, USA, 2002. % vor jede Referenz Kandler, K., Benker, N., Bundke, U., Cuevas, E., Ebert, M., Knippertz, P., Rodriguez, S., Schutz, L., and Weinbruch, S.: Chemical composition and complex refractive index of Saharan Mineral Dust at Izana, Tenerife (Spain) derived by electron microscopy, Atmos. Environ., 41, 8058–8074, 2007. % vor jede Referenz 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.: 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, 61, 32–50, 2009. % vor jede Referenz Kandler, K., Lieke, K., Benker, N., Emmel, C., Küpper, M., Müller-Ebert, D., Ebert, M., Scheuvens, D., Schladitz, A., Schütz, L., and Weinbruch, S.: Electron microscopy of particles collected at Praia, Cape Verde, during the Saharan Mineral Dust Experiment: particle chemistry, shape, mixing state and complex refractive index, Tellus B, 63, 475–496, 2011. % vor jede Referenz Karickhoff, S. W. and Bailey, G. W., Optical Absorption Spectra of Clay-Minerals, Clay Clay Miner., 21, 59–70, 1973. % vor jede Referenz Kokhanovsky, A. A. and Zege, E. P.: Local Optical-Parameters of Spherical Polydispersions – Simple Approximations, Appl. Optics, 34, 5513–5519, 1995. % vor jede Referenz Lafon, S., Rajot, J. L., Alfaro, S. C., and Gaudichet, A.: Quantification of iron oxides in desert aerosol, Atmos. Environ., 38, 1211–1218, 2004. % vor jede Referenz Lafon, S., Sokolik, I. N., Rajot, J. L., Caquineau, S., and Gaudichet, A.: Characterization of iron oxides in mineral dust aerosols: Implications for light absorption, J. Geophys. Res.-Atmos., 111, D21207, http://dx.doi.org/10.1029/2005JD007016doi:10.1029/2005JD007016, 2006. % vor jede Referenz Lieke, K., Kandler, K., Scheuvens, D., Emmel, C., Von Glahn, C., Petzold, A., Weinzierl, B., Veira, A., Ebert, M., Weinbruch, S., and Schütz, L.: Particle chemical properties in the vertical column based on aircraft observations in the vicinity of Cape Verde Islands, Tellus B, 63, 497–511, 2011. % vor jede Referenz Linke, C., Möhler, O., Veres, A., Mohácsi, Á., Bozóki, Z., Szabó, G., and Schnaiter, M.: Optical properties and mineralogical composition of different Saharan mineral dust samples: a laboratory study, Atmos. Chem. Phys., 6, 3315–3323, http://dx.doi.org/10.5194/acp-6-3315-2006doi:10.5194/acp-6-3315-2006, 2006. % vor jede Referenz Macke, A., Mueller, J., and Raschke, E.: Single scattering properties of atmospheric ice crystals, J. Atmos. Sci., 53, 2813–2825, 1996. % vor jede Referenz Meland, B., Kleiber, P. D., Grassian, V. H., and Young, M. A.: Visible light scattering study at 470, 550, and 660 nm of components of mineral dust aerosol: Hematite and goethite, J. Quant. Spectrosc. Ra., 112, 1108–1118, 2011. % vor jede Referenz Meng, Z. K., Yang, P., Kattawar, G. W., Bi, L., Liou, K. N., and Laszlo, I.: Single-scattering properties of tri-axial ellipsoidal mineral dust aerosols: A database for application to radiative transfer calculations, J. Aerosol Sci., 41, 501–512, 2010. % vor jede Referenz Merikallio, S., Lindqvist, H., Nousiainen, T., and Kahnert, M.: Modelling light scattering by mineral dust using spheroids: assessment of applicability, Atmos. Chem. Phys., 11, 5347–5363, http://dx.doi.org/10.5194/acp-11-5347-2011doi:10.5194/acp-11-5347-2011, 2011. % vor jede Referenz Mishchenko, M. I. and Travis, L. D.: Capabilities and limitations of a current FORTRAN implementation of the T-matrix method for randomly oriented, rotationally symmetric scatterers, J. Quant. Spectrosc. Ra., 60, 309–324, 1998. % vor jede Referenz Mishchenko, M. I., Travis, L. D., Kahn, R. A., and West, R. A.: Modeling phase functions for dustlike tropospheric aerosols using a shape mixture of randomly oriented polydisperse spheroids, J. Geophys. Res.-Atmos., 102, 16831–16847, 1997. % vor jede Referenz Mogili, P. K., Yang, K. H., Young, M. A., Kleiber, P. D., and Grassian, V. H.: Environmental aerosol chamber studies of extinction spectra of mineral dust aerosol components: Broadband IR-UV extinction spectra, J. Geophys. Res.-Atmos., 112, D21204, http://dx.doi.org/10.1029/2007JD008890doi:10.1029/2007JD008890, 2007. % vor jede Referenz Moore, D. M. and Reynolds, R. C. J.: X-Ray Diffraction and the Identification and Analysis of Clay Minerals, Oxford University Press, Oxford, New York, 1997. % vor jede Referenz Müller, D., Weinzierl, B., Petzold, A., Kandler, K., Ansmann, A., Müller, T., Tesche, M., Freudenthaler, V., Esselborn, M., Heese, B., Althausen, D., Schladitz, A., Otto, S., and Knippertz, P.: Mineral dust observed with AERONET Sun photometer, Raman lidar, and in situ instruments during SAMUM 2006: Shape-independent particle properties, J. Geophys. Res.-Atmos., 115, D07202, http://dx.doi.org/10.1029/2009JD012520doi:10.1029/2009JD012520, 2010. % vor jede Referenz Müller, T., Schladitz, A., Massling, A., Kaaden, N., Kandler, K., and Wiedensohler, A.: Spectral absorption coefficients and imaginary parts of refractive indices of Saharan dust during SAMUM-1, Tellus B, 61, 79–95, 2009. % vor jede Referenz Müller, T., Schladitz, A., Kandler, K., and Wiedensohler, A.: Spectral particle absorption coefficients, single scattering albedos, and imaginary parts of refractive indices from ground based in-situ measurements at Cape Verde Island during SAMUM-2, Tellus B, 63, 573–588, 2011. % vor jede Referenz Otto, S., Bierwirth, E., Weinzierl, B., Kandler, K., Esselborn, M., Tesche, M., Schladitz, A., Wendisch, M., and Trautmann, T.: Solar radiative effects of a Saharan dust plume observed during SAMUM assuming spheroidal model particles, Tellus B, 61, 270–296, 2009. % vor jede Referenz Petzold, A., Rasp, K., Weinzierl, B., Esselborn, M., Hamburger, T., Dornbrack, A., Kandler, K., Schutz, L., Knippertz, P., Fiebig, M., and Virkkula, A.: Saharan dust absorption and refractive index from aircraft-based observations during SAMUM 2006, Tellus B, 61, 118–130, 2009. % vor jede Referenz Press, W. H., Teukolsky, S. A., Vetterling, W. T., and Flannery, B. P.: Numerical Recipes in C: The Art of Scientific Computing, Cambridge University Press, Cambridge, 1992. % vor jede Referenz Querry, M. R.: Optical constants of minerals and other materials from the millimeter to the UV, Rep. CRDEC-CR-88009, US Army, Aberdeen, MD, 1987. % vor jede Referenz Reid, J. S., Jonsson, H. H., Maring, H. B., Smirnov, A., Savoie, D. L., Cliff, S. S., Reid, E. A., Livingston, J. M., Meier, M. M., Dubovik, O., and Tsay, S. C.: Comparison of size and morphological measurements of coarse mode dust particles from Africa, J. Geophys. Res.-Atmos., 108, 8593, http://dx.doi.org/10.1029/2002JD002485doi:10.1029/2002JD002485, 2003. % vor jede Referenz Scheuvens, D., Kandler, K., Küpper, M., Lieke, K., Zorn, S., Ebert, M., Schütz, L., and Weinbruch, S.: Indiviual-particle analysis of airborne dust samples collected over Morocco in 2006 during SAMUM 1, Tellus B, 63, 512–530, 2011. % vor jede Referenz Schladitz, A., Müller, T., Kaaden, N., Massling, A., Kandler, K., Ebert, M., Weinbruch, S., Deutscher, C., and Wiedensohler, A.: In situ measurements of optical properties at Tinfou (Morocco) during the Saharan Mineral Dust Experiment SAMUM 2006, Tellus B, 61, 64–78, 2009. % vor jede Referenz Schnaiter, M., Schmid, O., Petzold, A., Fritzsche, L., Klein, K. F., Andreae, M. O., Helas, G., Thielmann, A., Gimmler, M., Möhler, O., Linke, C., and Schurath, U.: Measurement of wavelength-resolved light absorption by aerosols utilizing a UV-VIS extinction cell, Aerosol Sci. Technol., 39, 249–260, 2005. % vor jede Referenz Sokolik, I., Andronova, A., and Johnson, T. C.: Complex Refractive-Index of Atmospheric Dust Aerosols, Atmos. Environ A-Gen., 27, 2495–2502, 1993. % vor jede Referenz Sokolik, I. N. and Toon, O. B.: Incorporation of mineralogical composition into models of the radiative properties of mineral aerosol from UV to IR wavelengths, J. Geophys. Res.-Atmos., 104, 9423–9444, 1999. % vor jede Referenz Wagner, R., Linke, C., Naumann, K. H., Schnaiter, M., Vragel, M., Gangl, M., and Horvath, H.: A review of optical measurements at the aerosol and cloud chamber AIDA, J. Quant. Spectrosc. Ra., 110, 930–949, 2009. % vor jede Referenz Wagner, R., Ajtai, T., Kandler, K., Lieke, K., Linke, C., Müller, T., Schnaiter, M., and Vragel, M.: Complex refractive indices of Saharan dust samples at visible and near UV wavelengths: a laboratory study, Atmos. Chem. Phys. Discuss., 11, 21363–21427, http://dx.doi.org/10.5194/acpd-11-21363-2011doi:10.5194/acpd-11-21363-2011, 2011. % vor jede Referenz Wiegner, M., Gasteiger, J., Kandler, K., Weinzierl, B., Rasp, K., Esselborn, M., Freudenthaler, V., Heese, B., Toledano, C., Tesche, M., and Althausen, D.: Numerical simulations of optical properties of Saharan dust aerosols with emphasis on lidar applications, Tellus B, 61, 180–194, 2009. % vor jede Referenz WMO: World Climate Program (WCP)/IAMAP, A preliminary cloudless standard atmosphere for radiation computation, WMO, Geneva, 1986. % vor jede Referenz Yang, P., Feng, Q., Hong, G., Kattawar, G. W., Wiscombe, W. J., Mishchenko, M. I., Dubovik, O., Laszlo, I., and Sokolik, I. N.: Modeling of the scattering and radiative properties of nonspherical dust-like aerosols, J. Aerosol Sci., 38, 995–1014, 2007. % vor jede Referenz Zakharova, N. T. and Mishchenko, M. I.: Scattering properties of needlelike and platelike ice spheroids with moderate size parameters, Appl. Optics, 39, 5052–5057, 2000.