Modeling the single and multiple scattering properties of soot-laden mineral dust aerosols

Xu, Guanglang; Stegmann, Patrick G.; Brooks, Sarah D.; Yang, Ping

doi:10.1364/oe.25.00a990

Cited by 14 publications

(6 citation statements)

References 44 publications

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“…With an average over the aggregate size, the empirical approximation should give even better approximations. The bulk MEC and MAC are approximately 7 and 6 m 2 g −1 , respectively, at 500 nm, which is in reasonable agreement with observations (Bond and Bergstrom, 2006;Kahnert et al, 2010;Liu et al, 2010;Xu et al, 2017). The empirical results overestimate MEC and MAC of polydispersity by 3.7 % and 4.9 %, respectively, and underestimate those of necking by 3.6 % and 2.8 %.…”

Section: Effects Of Minor Structuressupporting

confidence: 88%

Accounting for the effects of nonideal minor structures on the optical properties of black carbon aerosols

et al. 2019

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Abstract. Black carbon (BC) aerosol is the strongest sunlight-absorbing aerosol, and its optical properties are fundamental to radiative forcing estimations and retrievals of its size and concentration. BC particles exist as aggregate structures with small monomers and are widely represented by the idealized fractal aggregate model. In reality, BC particles possess complex and nonideal minor structures besides the overall aggregate structure, altering their optical properties in unforeseen ways. This study introduces the parameter “volume variation” to quantify and unify different minor structures and develops an empirical relationship to account for their effects on BC optical properties from those of ideal aggregates. Minor structures considered are as follows: the polydispersity of monomer size, the irregularity and coating of the individual monomer, and necking and overlapping among monomers. The discrete dipole approximation is used to calculate the optical properties of aggregates with these minor structures. Minor structures result in scattering cross-section enhancement slightly more than that of absorption cross section, and their effects on the angle-dependent phase matrix as well as asymmetry factor are negligible. As expected, the effects become weaker with the increase in wavelength. Our results suggest that a correction ratio of 1.05 is necessary to account for the mass or volume normalized absorption and scattering of nonideal aggregates in comparison to ideal ones, which also applies to aggregates with multiple minor structures. In other words, the effects of minor structures are mainly contributed by their influence on particle volume/mass that cannot be ignored, and a relative difference of approximately 5 % is noticed after removing the volume effects. Thus, accurate knowledge and evaluation of BC volume/mass are more important than those of the minor structures themselves. Most importantly, the simulations of optical properties of nonideal aggregates are greatly simplified by applying the empirical relationship because they can be directly obtained from those of the corresponding ideal aggregates, a volume/mass difference parameter, and the correction factor, i.e., 1.05, not the detailed minor structure information. We expect this convenient treatment to find wide applications for the accounting for the effects of nonideal minor structures on BC optical properties.

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Section: Effects Of Minor Structuressupporting

confidence: 88%

Accounting for the effects of nonideal minor structures on the optical properties of black carbon aerosols

et al. 2019

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“…With an average over the aggregate size, the empirical approximation should give even better approximations. The bulk MEC and MAC are approximately 7 and 6 m 2 g -1 , respectively, at 500 nm, which is in reasonable agreement with observations (Bond and Bergstrom, 2006;Kahnert et al, 2010;Liu et al, 2010;Xu et al, 2017). The empirical results overestimate MEC and MAC of polydispersity by 2.8 % and 3.7 %, respectively, and underestimate those of necking by 4.5 % and 3.9 %.…”

Section: Effects Of Minor Structuressupporting

confidence: 87%

Accounting for the effects of non-ideal minor structures on the optical properties of black carbon aerosols

Teng¹,

Liu²,

Schnaiter³

et al. 2018

Preprint

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<p><strong>Abstract.</strong> Black carbon (BC) aerosol is the strongest sunlight-absorbing aerosol, and its optical properties are fundamental to radiative forcing estimations and retrievals of its size and concentration. During incomplete combustion, BC particles exist as aggregate structures with small monomers, which are widely represented by the idealized fractal aggregate model formed by monodisperse spherical monomers in point-contact. In reality, BC particles possess complex and non-ideal minor structures besides the overall aggregate structure, altering its optical properties in unforeseen ways. This study introduces a parameter <q>volume variation</q> to quantify and unify different minor structures, and develops an empirical relation to account for their effects on BC optical properties from those of ideal aggregates. Minor structures considered are the polydispersity of monomer size, irregularity and coating of individual monomer, and necking and overlapping among monomers. The discrete dipole approximation is used to calculate the optical properties of aggregates with these minor structures. Minor structures result in scattering cross section enhancement slightly more than that of absorption cross section, and their effects become weaker with the increase of wavelength. Their effects on the angular-dependent phase matrix as well as asymmetry factor are negligible. Our results suggest that a correction ratio of 1.05 is necessary to account for the mass/volume normalized absorption and scattering of non-ideal aggregates in comparison to ideal ones. In other words, minor structures tend to enhance the BC mass absorption and scattering by 5&#8201;%, which also applies to aggregates with multiple minor structures. The simulations of optical properties of non-ideal aggregates are greatly simplified, because they can be directly obtained from those of the corresponding ideal aggregates. We expect this generalized correction to find wide use for modeling realistic BC aggregates due to the simplicity involved in generating ideal fractal aggregates, and it is of great value for not only interpretation of measurements but also practical modeling that requires large amount of simulations.</p>

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“…To account for irregular geometries, multiple numerical models are available for calculating the single-scattering properties of nonspherical particles (Yang and Liou, 1996a;Mishchenko et al, 1997;Yurkin and Hoekstra, 2011;Bi et al, 2013). Following Liu et al (2013), this study uses a combination of the pseudospectral time domain (PSTD) method (Liu, 1997;Liu et al, 2012) and the improved geometric-optics method (IGOM; Yang and Liou, 1996b;Yang and Liou, 1998;Bi et al, 2014) to cover the required range of dust size parameters at visible incident wavelengths.…”

Section: Methodsmentioning

confidence: 99%

Scattering matrices of mineral dust aerosols: a refinement of the refractive index impact

et al. 2020

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Mineral dust, as one of the most important aerosols, plays a crucial role in the atmosphere by directly interacting with radiation, while there are significant uncertainties in determining dust optical properties to quantify radiative effects and to retrieve their properties. Laboratory and in situ measurements of the refractive indices (RIs) of dust differ, and different RIs have been applied in numerical studies used for model developments, aerosol retrievals, and radiative forcing simulations. This study reveals the importance of the dust RI for the development of a model of dust optical properties. The Koch-fractal polyhedron is used as the modeled geometry, and the pseudospectral time domain method and improved geometric-optics method are combined for optical property simulations over the complete size range. We find that the scattering matrix elements of different kinds of dust particles are reasonably reproduced by choosing appropriate RIs, even when using a fixed particle geometry. The uncertainty of the RI would greatly affect the determination of the geometric model, as a change in the RI, even in the widely accepted RI range, strongly affects the shape parameters used to reproduce the measured dust scattering matrix elements. A further comparison shows that the RI influences the scattering matrix elements in a different way than geometric factors, and, more specifically, the P 11 , P 12 , and P 22 elements seem more sensitive to the RI of dust. In summary, more efforts should be devoted to account for the uncertainties on the dust RI in modeling its optical properties, and the development of corresponding optical models can potentially be simplified by considering only variations over differ-ent RIs. Considerably more research, especially from direct measurements, should be carried out to better constrain the uncertainties related to the dust aerosol RIs.

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Modeling the single and multiple scattering properties of soot-laden mineral dust aerosols

Cited by 14 publications

References 44 publications

Accounting for the effects of nonideal minor structures on the optical properties of black carbon aerosols

Accounting for the effects of nonideal minor structures on the optical properties of black carbon aerosols

Accounting for the effects of non-ideal minor structures on the optical properties of black carbon aerosols

Scattering matrices of mineral dust aerosols: a refinement of the refractive index impact

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