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On the impact of non-sphericity and small-scale surface roughness on the optical properties of hematite aerosols
SMHI, Research Department, Air quality.ORCID iD: 0000-0001-5695-1356
2011 (English)In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 112, no 11, 1815-1824 p.Article in journal (Refereed) Published
Abstract [en]

We perform a comparative modelling study to investigate how different morphological features influence the optical properties of hematite aerosols. We consider high-order Chebyshev particles as a proxy for aerosol with a small-scale surface roughness, and spheroids as a model for nonspherical aerosols with a smooth boundary surface. The modelling results are compared to those obtained for homogeneous spherical particles. It is found that for hematite particles with an absorption efficiency of order unity the difference in optical properties between spheres and spheroids disappears. For optically softer particles, such as ice particles at far-infrared wavelengths, this effect can be observed for absorption efficiencies lower than unity. The convergence of the optical properties of spheres and spheroids is caused by absorption and quenching of internal resonances inside the particles, which depend both on the imaginary part of the refractive index and on the size parameter, and to some extent on the real part of the refractive index. By contrast, small-scale surface roughness becomes the dominant morphological feature for large particles. This effect is likely to depend on the amplitude of the surface roughness, the relative significance of internal resonances, and possibly on the real part of the refractive index. The extinction cross section is rather insensitive to surface roughness, while the single-scattering albedo, asymmetry parameter, and the Mueller matrix are strongly influenced. Small-scale surface roughness reduces the backscattering cross section by up to a factor of 2-3 as compared to size-equivalent particles with a smooth boundary surface. This can have important implications for the interpretation of lidar backscattering observations. (C) 2011 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
2011. Vol. 112, no 11, 1815-1824 p.
Keyword [en]
Scattering, Aerosols, T-matrix, Surface roughness, Hematite, Lidar
National Category
Meteorology and Atmospheric Sciences
Research subject
Environment
Identifiers
URN: urn:nbn:se:smhi:diva-515DOI: 10.1016/j.jqsrt.2011.01.022ISI: 000292533900023OAI: oai:DiVA.org:smhi-515DiVA: diva2:806047
Conference
12th International Conference on Electromagnetic and Light Scattering by Nonspherical Particles - Theory, Measurements, and Applications, JUN 28-JUL 02, 2010, Helsinki, FINLAND
Available from: 2015-04-17 Created: 2015-04-15 Last updated: 2017-12-04Bibliographically approved

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Kahnert, Michael

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