A comparison of solutions for light scattering and absorption by agglomerated or arbitrarily-shaped particles

Ku, Jerry C.; Shim, Kyoung Hoon

doi:10.1016/0022-4073(92)90029-4

Cited by 60 publications

(19 citation statements)

References 30 publications

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“…But, near the fire source particle asymentry can have some impact on particle properties. While aerosol extinction efficiency is more or less conserved, aggregation can increase total scattering relative to absorption, increase the asymmetry parameter, and depolarize scattered light (Ku and Shim, 1992;Colbeck et al, 1997;Sorensen, 2001). Consequently, such particles cannot be modeled as equivalent spheres.…”

Section: Direct Forward Methodsmentioning

confidence: 99%

A review of biomass burning emissions part III: intensive optical properties of biomass burning particles

Reid¹,

et al. 2005

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Abstract. Because of its wide coverage over much of the globe, biomass burning has been widely studied in the context of direct radiative forcing. Such study is warranted as smoke particles scatter and at times absorb solar radiation efficiently. Further, as much of what is known about smoke transport and impacts is based on remote sensing measurements, the optical properties of smoke particles have far reaching effects into numerous aspects of biomass burning studies. Global estimates of direct forcing have been widely varying, ranging from near zero to −1 W m −2 . A significant part of this difference can be traced to varying assumptions on the optical properties of smoke. This manuscript is the third part of four examining biomass-burning emissions. Here we review and discuss the literature concerning measurement and modeling of optical properties of biomassburning particles. These include available data from published sensitivity studies, field campaigns, and inversions from the Aerosol Robotic Network (AERONET) of Sun photometer sites. As a whole, optical properties reported in the literature are varied, reflecting both the dynamic nature of fires, variations in smoke aging processes and differences in measurement technique. We find that forward modeling or "internal closure" studies ultimately are of little help in resolving outstanding measurement issues due to the high degree of degeneracy in solutions when using "reasonable" input parameters. This is particularly notable with respect to index of refraction and the treatment of black carbon. Consequently, previous claims of column closure may in fact be more ambiguous. Differences between in situ and retrieved ω o values have implications for estimates of mass scattering and mass absorption efficiencies. In this manuscript we Correspondence to: J. S. Reid (reidj@nrlmry.navy.mil) review and discuss this community dataset. Strengths and lapses are pointed out, future research topics are prioritized, and best estimates and uncertainties of key smoke particle parameters are provided.

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Section: Direct Forward Methodsmentioning

confidence: 99%

A review of biomass burning emissions part III: intensive optical properties of biomass burning particles

Reid¹,

et al. 2005

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“…Ku and Shim (1992) did a nice job of reviewing this subject up to 1992 and have also made detailed comparisons of three prominent electromagnetic approaches to this problem. The oldest approach is that of Jones (1979), which is based on an original formulation derived from Maxwell's equations by Saxon (1974).…”

Section: Geometric Aggregate Light Scatteringmentioning

confidence: 99%

Light Scattering by Fractal Aggregates: A Review

Sorensen

2001

Aerosol Science and Technology

1,035

756

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This paper presents a review of scattering and absorption of light by fractal aggregates. The aggregates are typically diffusion limited cluster aggregates (DLCA) with fractal dimensions of D ' 1:75, which occur frequently in aerosols and colloids, but other types of aggregates are discussed as well. The results of the review are quite general. A scaling description of the scattering of waves forms the basis of our understanding. This description yields the optical structure factor S(q ) of the aggregate, where q is the scattering wavevector, a key quantity. The rigorous approach to the structure factor, the Fourier transform of the density correlation function, is also given and various forms provided in the literature are compared and the best selected. Light scattering is directly related to the structure factor under the assumption of no internal multiple scattering. This so-called Rayleigh -Debye -Gans (RDG) approximation is compared to more rigorous electromagnetic approaches and found to be quite accurate for fractal aggregates. This results despite the presence of internal multiple scattering, which leads to depolarization, and which is also extensively described. For ensembles of aggregates, the effects of aggregate polydispersity on scattering experiments are described and methods for proper analysis are given. A description of optical particle sizing and morphology analysis is given for a complete in situ characterization of the aggregate system. The review relies strongly on straightforward physical reasoning and experimental examples, largely from aerosols, especially those of carbonaceous soot. This paper not only reviews and consolidates, but also presents new results including a scaling analysis of multiple scattering, which leads to depolarization, with a successful comparison to available data and an understanding of structural subtleties; demonstration of the signi cance of a phase shift parameter for evaluating the range of validity of the RDG theory; a Maxwell -Garnet analysis of fractal aggregate scattering; calculations of the albedo and successful comparison to available simulation data; and speculations on multiple scattering and the interior eld. INTRODUCTIONThe purpose of this review is to unify our knowledge of how fractal aggregates scatter (and absorb) light. This is of value for light scattering diagnostics of aerosols and colloids and for understanding the optics of these systems in the environment. The subject has seen able and useful reviews before by Teixeira (1986), Martin and Hurd (1987), Charalampopoulos (1992), and a brief overview by myself (Sorensen 1997). Very recently Fuller and Mackowski (2000) have given an excellent review of the superposition theory of scattering from aggregates. My desire here is to provide an up-to-date and comprehensive review useful for the experimentalist. Any theory that does appear will be based on simple physical arguments rather than detailed mathematical analysis. Many of the general results to be described here apply to nonfractal aggreg...

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“…We can obtain a further reduction in order for sphere pairs by formally factoring out one of the sets of scattering coefficients in Eq. (13 …”

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confidence: 99%

Calculation of total cross sections of multiple-sphere clusters

1994

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A method for calculating the extinction, absorption, and scattering cross sections of clusters of neighboring spheres for both fixed and random orientations is developed. The analysis employs the superposition formulation for radiative interactions among spheres, in which the total field from the cluster is expressed as a superposition of vector spherical harmonic expansions about each of the spheres in the cluster. Through the use of addition theorems a matrix equation for the expansion coefficients is obtained. Further application of addition theorems on the inverse of the coefficient matrix is shown to yield analytical expressions for the orientation-averaged total cross sections of the sphere cluster. Calculations of the cross sections of pairs of spheres and fractal aggregates of several spheres are presented. It is found that a dipole representation of the field in each sphere does not adequately predict the absorption cross section of clusters of small-size-parameter spheres when the spheres are highly conducting. For this situation several multipole orders are required for an accurate calculation of the absorption cross section. In addition, the predicted absorption of sphere clusters can be significantly greater than that estimated from the sum of the isolated-sphere cross sections.

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A comparison of solutions for light scattering and absorption by agglomerated or arbitrarily-shaped particles

Cited by 60 publications

References 30 publications

A review of biomass burning emissions part III: intensive optical properties of biomass burning particles

A review of biomass burning emissions part III: intensive optical properties of biomass burning particles

Light Scattering by Fractal Aggregates: A Review

Calculation of total cross sections of multiple-sphere clusters

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