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Article

Scattering and Radiative Properties of Morphologically Complex Carbonaceous Aerosols: A Systematic Modeling Study

by 1,2 and 3,*
1
NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
2
Columbia University, 2880 Broadway, New York, NY 10025, USA
3
NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
*
Author to whom correspondence should be addressed.
Remote Sens. 2018, 10(10), 1634; https://doi.org/10.3390/rs10101634
Received: 8 September 2018 / Revised: 4 October 2018 / Accepted: 6 October 2018 / Published: 14 October 2018
This paper provides a thorough modeling-based overview of the scattering and radiative properties of a wide variety of morphologically complex carbonaceous aerosols. Using the numerically-exact superposition T-matrix method, we examine the absorption enhancement, absorption Ångström exponent (AAE), backscattering linear depolarization ratio (LDR), and scattering matrix elements of black-carbon aerosols with 11 different model morphologies ranging from bare soot to completely embedded soot–sulfate and soot–brown carbon mixtures. Our size-averaged results show that fluffy soot particles absorb more light than compact bare-soot clusters. For the same amount of absorbing material, the absorption cross section of internally mixed soot can be more than twice that of bare soot. Absorption increases as soot accumulates more coating material and can become saturated. The absorption enhancement is affected by particle size, morphology, wavelength, and the amount of coating. We refute the conventional belief that all carbonaceous aerosols have AAEs close to 1.0. Although LDRs caused by bare soot and certain carbonaceous particles are rather weak, LDRs generated by other soot-containing aerosols can reproduce strong depolarization measured by Burton et al. for aged smoke. We demonstrate that multi-wavelength LDR measurements can be used to identify the presence of morphologically complex carbonaceous particles, although additional observations can be needed for full characterization. Our results show that optical constants of the host/coating material can significantly influence the scattering and absorption properties of soot-containing aerosols to the extent of changing the sign of linear polarization. We conclude that for an accurate estimate of black-carbon radiative forcing, one must take into account the complex morphologies of carbonaceous aerosols in remote sensing studies as well as in atmospheric radiation computations. View Full-Text
Keywords: carbonaceous aerosols; scattering matrix; polarization; depolarization; absorption carbonaceous aerosols; scattering matrix; polarization; depolarization; absorption
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MDPI and ACS Style

Liu, L.; Mishchenko, M.I. Scattering and Radiative Properties of Morphologically Complex Carbonaceous Aerosols: A Systematic Modeling Study. Remote Sens. 2018, 10, 1634. https://doi.org/10.3390/rs10101634

AMA Style

Liu L, Mishchenko MI. Scattering and Radiative Properties of Morphologically Complex Carbonaceous Aerosols: A Systematic Modeling Study. Remote Sensing. 2018; 10(10):1634. https://doi.org/10.3390/rs10101634

Chicago/Turabian Style

Liu, Li, and Michael I. Mishchenko. 2018. "Scattering and Radiative Properties of Morphologically Complex Carbonaceous Aerosols: A Systematic Modeling Study" Remote Sensing 10, no. 10: 1634. https://doi.org/10.3390/rs10101634

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