Atmos. Chem. Phys. Discuss., 13, 18451-18488, 2013
www.atmos-chem-phys-discuss.net/13/18451/2013/
doi:10.5194/acpd-13-18451-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Single scattering by realistic, inhomogeneous mineral dust particles with stereogrammetric shapes
H. Lindqvist1, O. Jokinen2, K. Kandler3, D. Scheuvens3, and T. Nousiainen1
1University of Helsinki, Department of Physics, Helsinki, Finland
2Aalto University, Department of Real Estate, Planning and Geoinformatics, Espoo, Finland
3Technische Universität Darmstadt, Inst. für Angewandte Geowissenschaften, Darmstadt, Germany

Abstract. Light scattering by single, inhomogeneous mineral dust particles was simulated based on shapes and compositions derived directly from measurements of real dust particles instead of using a mathematical shape model. We demonstrate the use of stereogrammetric shape retrieval method in the context of single-scattering modelling of mineral dust for four different dust types – all of them inhomogeneous – ranging from compact, equidimensional shapes to very elongated and aggregate shapes. The three-dimensional particle shapes were derived from stereo pairs of scanning-electron microscope images, and inhomogeneous composition was determined by mineralogical interpretation of localized elemental information based on energy-dispersive spectroscopy. Scattering computations were performed for particle equal-volume diameters from 0.08 μm up to 2.8 μm at 550 nm wavelength, using the discrete-dipole approximation. Particle-to-particle variation in scattering by mineral dust was found to be quite considerable and was not well reproduced by simplified shapes of homogeneous spheres, spheroids, or Gaussian random spheres. Effective-medium approximation results revealed that particle inhomogeneity should be accounted even for small amounts of absorbing media (here up to 2% of the volume), especially when considering scattering by inhomogeneous particles at size parameters 3<x<8. When integrated over a lognormal size distribution, the linear depolarization ratio and single-scattering albedo were also found to be sensitive to inhomogeneity. The methodology applied is work-intensive and the light-scattering method used is quite limited in terms of size parameter coverage. It would therefore be desirable to find sufficiently accurate but simpler approach with fewer limitations for single-scattering modelling of dust. Our results could be invaluable as references in validation of such a method.

Citation: Lindqvist, H., Jokinen, O., Kandler, K., Scheuvens, D., and Nousiainen, T.: Single scattering by realistic, inhomogeneous mineral dust particles with stereogrammetric shapes, Atmos. Chem. Phys. Discuss., 13, 18451-18488, doi:10.5194/acpd-13-18451-2013, 2013.
 
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