ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-1527-2011 A sensitivity study on the effects of particle chemistry, asphericity and size on the mass extinction efficiency of mineral dust in the earth's atmosphere: from the near to thermal IR Hansell Jr. R. A. 1 3 Reid J. S. 2 Tsay S. C. 3 Roush T. L. 4 Kalashnikova O. V. 5 University of Maryland, College Park, Maryland, USA Naval Research Laboratory, Monterey, California, USA Goddard Space Flight Center, NASA, Greenbelt, Maryland, USA NASA Ames, Research Center, Moffett Field, California, USA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA 17 02 2011 11 4 1527 1547 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/11/1527/2011/acp-11-1527-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/1527/2011/acp-11-1527-2011.pdf

To determine a plausible range of mass extinction efficiencies (MEE) of terrestrial atmospheric dust from the near to thermal IR, sensitivity analyses are performed over an extended range of dust microphysical and chemistry perturbations. The IR values are subsequently compared to those in the near-IR, to evaluate spectral relationships in their optical properties. Synthesized size distributions consistent with measurements, model particle size, while composition is defined by the refractive indices of minerals routinely observed in dust, including the widely used OPAC/Hess parameterization. Single-scattering properties of representative dust particle shapes are calculated using the T-matrix, Discrete Dipole Approximation and Lorenz-Mie light-scattering codes. For the parameterizations examined, MEE ranges from nearly zero to 1.2 m<sup>2</sup> g<sup>−1</sup>, with the higher values associated with non-spheres composed of quartz and gypsum. At near-IR wavelengths, MEE for non-spheres generally exceeds those for spheres, while in the thermal IR, shape-induced changes in MEE strongly depend on volume median diameter (VMD) and wavelength, particularly for MEE evaluated at the mineral resonant frequencies. MEE spectral distributions appear to follow particle geometry and are evidence for shape dependency in the optical properties. It is also shown that non-spheres best reproduce the positions of prominent absorption peaks found in silicates. Generally, angular particles exhibit wider and more symmetric MEE spectral distribution patterns from 8–10 μm than those with smooth surfaces, likely due to their edge-effects. Lastly, MEE ratios allow for inferring dust optical properties across the visible-IR spectrum. We conclude the MEE of dust aerosol are significant for the parameter space investigated, and are a key component for remote sensing applications and the study of direct aerosol radiative effects.

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