ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-5347-2011 Modelling light scattering by mineral dust using spheroids: assessment of applicability Merikallio S. 1 Lindqvist H. 2 Nousiainen T. 2 Kahnert M. 3 Climate Change, Finnish Meteorological Institute, P.O. Box 503, 00101 Finland Department of Physics, University of Helsinki, P.O. Box 48, 00014 Finland Swedish Meteorological and Hydrological Institute, Folkborgsvägen 1, 601 76 Norrköping, Sweden 09 06 2011 11 11 5347 5363 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/11/5347/2011/acp-11-5347-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/5347/2011/acp-11-5347-2011.pdf

We study the applicability of spheroidal model particles for simulating the single-scattering optical properties of mineral dust aerosols. To assess the range of validity of this model, calculations are compared to laboratory observations for five different dust samples at two wavelengths. We further investigate whether the best-fit shape distributions of spheroids for different mineral dust samples have any similarities that would allow us to suggest a generic first-guess shape distribution for suspended mineral dust. We find that best-fit shape distributions vary considerably between samples and even between wavelengths, making definitive suggestions for a shape distribution difficult. The best-fit shape distribution also depends strongly on the refractive index assumed and the cost function adopted. However, a power-law shape distribution which favours those spheroids that depart most from the spherical shape is found to work well in most cases. To reproduce observed asymmetry parameters, best results are obtained with a power-law shape distribution with an exponent around three.

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