Light scattering and absorption by fractal aggregates including soot

Sorensen, Christopher M.; Yon, Jérôme; Liu, Fengshan; Maughan, Justin B.; Heinson, William R.; Berg, Matthew J.

doi:10.1016/j.jqsrt.2018.05.016

Cited by 65 publications

(46 citation statements)

References 44 publications

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“…By fitting our model to experimental data (purple solid line), we can estimate the following parameters: d f = 1.6; a=30 nm; k 0 = 1.3; and n = 1.8 + 0.3 i . Although we are not able to test each of these parameters independently, their values agree with data in recent literature (e.g., see Doner and Liu (2017) and Sorensen et al (2018)). The model outlined above is in good agreement with simulations generated using the same parameters, shown in Fig.…”

Section: Resultssupporting

confidence: 83%

“…For example, absorption in a dust grain is a property for which its chemical composition only gives a rough estimate, mainly due to the influence of surface and density inhomogeneities. Similarly, changes in the optical properties of dust grains due to their internal structure depend on whether they are dielectric or absorbing (Voshchinnikov et al 2000;Sorensen 2001;Bohren and Huffman 2008;Sorensen et al 2018).…”

Section: Introductionmentioning

confidence: 99%

“…Alternatively, introducing parametrizations that are numerically much cheaper than the Mie expansion can strongly reduce computation times (Ghan and Zaveri 2007). However, many authors have called into question the validity of these assumptions, concluding that they should be discussed for each specific case (Pollack and Cuzzi 1980;Mishchenko et al 1995;Nousiainen et al 2011;Sorensen et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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Light extinction and scattering from aggregates composed of submicron particles

et al. 2020

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The influence of the internal structure of inhomogeneous particles on their radiative properties is an open issue repeatedly questioned in many fields of science and technology. The importance of a refined description of the particle composition and structure, going beyond mean-field approximations, is generally recognized. Here, we focus on describing internal inhomogeneities from a statistical point of view. We introduce an analytical description based on the two-point density-density correlation function, or the corresponding static structure factor, to calculate the extinction cross sections. The model agrees with numerical predictions and is validated experimentally with colloidal aggregates in the 0.3–6 μm size range, which serve as an inhomogeneous model system that can be characterized enough to work without any free parameters. The model can be tightly compared to measurements with single particle extinction and scattering and spectrophotometry and suggests a simple behavior for 90° scattering from fractal aggregates as a function of extinction, which is also confirmed experimentally and numerically. We also discuss the case of absorbing particles and report the experimental results for water suspensions of black carbon for both the forward and 90° scattering properties. In this case, the total scattering and the extinction cross sections determine the single scattering albedo, which agrees with numerical simulations. The three parameters necessary to feed radiative transfer models, namely, extinction, asymmetry parameter, and single scattering albedo, can all be set by the analytical model, with explicit dependence on a few parameters. Results are applicable to radiative transfer problems in climate, paleoclimate, star and planetary formation, and nanoparticle optical characterization for science and industry, including the intercomparison of different optical methods such as those adopted by ISO standards.

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Section: Resultssupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Light extinction and scattering from aggregates composed of submicron particles

et al. 2020

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“…The morphology of a dry BB aerosol as a fractal cluster is represented by a statistical scaling law [58,59] as:…”

Section: Theoretical Methodsmentioning

confidence: 99%

Refractive Indices of Biomass Burning Aerosols Obtained from African Biomass Fuels Using RDG Approximation

et al. 2020

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Biomass burning (BB) aerosols contribute to climate forcing, but much is still unknown about the extent of this forcing, owing partially to the high level of uncertainty regarding BB aerosol optical properties. A key optical parameter is the refractive index (RI), which influences the absorbing and scattering properties of aerosols. This quantity is not measured directly, but it is obtained by fitting the measured scattering cross section and extinction cross section to a theoretical model using the RI as a fitting parameter. We used the Rayleigh–Debye–Gans (RDG) approximation to retrieve the complex RI of freshly emitted BB aerosol from two fuels (eucalyptus and olive) from Africa in the spectral range of 500–580 nm. Experimental measurements were carried out using cavity ring-down spectroscopy to measure extinction over the range of wavelengths of 500–580 nm and nephelometry to measure scattering at three wavelengths of 450, 550, and 700 nm for size-selected BB aerosol particles. The fuels were combusted in a tube furnace at a temperature of 800 °C, which is representative of the flaming stage of burning. Filter samples were collected and imaged using tunneling electron microscopy to obtain information on the morphology and size of the particles, which was used in the RDG calculations. The mean radii of the monomers were 27.8 and 31.5 nm for the eucalyptus and the olive fuels, respectively. The components of the retrieved complex RI were in the range of 1.31 ≤ n ≤ 1.56 and 0.045 ≤ k ≤ 0.468. The real and complex parts of the RI increase with increasing particle mobility diameter. The real part of the RI is lower, and the imaginary part is higher than what was recommended in literature for black carbon generated by propane or field measurements from fires of mixed wood samples. Fuel dependent results from controlled laboratory experiments can be used in climate modeling efforts and to constrain field measurements from biomass burning.

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“…Thus, the arrangement of particles in the CCA model is random and the core particle does not exist in the aggregate as in the DLA model. According to the fractal theory, the morphology and construction of the aggregate can be described as (Sorensen, et al, 2018)…”

Section: Radiative Properties Of Soot Aggregatesmentioning

confidence: 99%

Investigation on the effect of fractal soot aggregation on radiative transfer in homogeneous gas-soot mixture using full-spectrum k-distribution method

Dong

Mao

et al. 2019

JTST

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The full-spectrum k-distribution (FSK) method and Generalized Multiparticle Mie-solution (GMM) method are applied to study the influences of soot aggregation on the radiative heat transfer in homogeneous gas-soot mixtures. The radiative transfer equation is solved by the finite volume method. The effect of soot aggregates with different fractal dimensions, monomer radiuses and the number of monomers on distributions of radiative heat flux and radiative heat source in the gas-soot mixture are studied, and the results show that increasing the fractal dimension, monomer radiuses, or decreasing the number of monomers will result in larger deviation between local radiative heat flux and radiative heat source of gas-soot mixture with soot aggregates and those with single soot particles. As a whole, the soot aggregation has a significant impact on the radiative heat transfer in the homogeneous gas-soot mixtures, and the effect of soot aggregation should better be considered as much as possible to obtain more accurate calculated results.

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Light scattering and absorption by fractal aggregates including soot

Cited by 65 publications

References 44 publications

Light extinction and scattering from aggregates composed of submicron particles

Light extinction and scattering from aggregates composed of submicron particles

Refractive Indices of Biomass Burning Aerosols Obtained from African Biomass Fuels Using RDG Approximation

Investigation on the effect of fractal soot aggregation on radiative transfer in homogeneous gas-soot mixture using full-spectrum k-distribution method

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