TY - JOUR

T1 - Performance of the discrete dipole approximation for optical properties of black carbon aggregates

AU - Liu, Chao

AU - Teng, Shiwen

AU - Zhu, Yingying

AU - Yurkin, Maxim A.

AU - Yung, Yuk L.

PY - 2018/12/1

Y1 - 2018/12/1

N2 - The optical properties of black carbon (BC) are fundamental for radiative transfer and remote sensing. BC geometry is successfully represented by an idealized model named “fractal aggregate” and numerous methods are available and widely used to simulate the corresponding optical properties. This study systematically evaluates the performance of the discrete dipole approximation (DDA) for optical simulations of BC aggregates. The Multiple Sphere T-Matrix (MSTM) results are used as references for accuracy evaluation. The differences between the DDA and MSTM can be controlled to be less than 3% by using dipole size much smaller than the monomer size, and the DDA efficiency is sensitive to aggregate structures, e.g. lacy or compact. We find that shape representation for small-sized monomers during DDA discretization leads significant errors, i.e., up to 10%, and relatively large refractive index of BC also affects the DDA accuracy. However, the MSTM treats the BC monomers as perfect spheres without overlapping, and the imperfect structure that is implicitly introduced in the DDA simulations due to the spatial discretization may be a better representation of realistic BC particles. Moreover, the accuracy and efficiency of the DDA can be improved by defining dipoles on the particle boundary to have refractive indices given by the effective medium approximation (EMA). This leads to the adequate shape representation even using larger dipole sizes, and results in the DDA accuracy comparable to that of the reference MSTM solution.

AB - The optical properties of black carbon (BC) are fundamental for radiative transfer and remote sensing. BC geometry is successfully represented by an idealized model named “fractal aggregate” and numerous methods are available and widely used to simulate the corresponding optical properties. This study systematically evaluates the performance of the discrete dipole approximation (DDA) for optical simulations of BC aggregates. The Multiple Sphere T-Matrix (MSTM) results are used as references for accuracy evaluation. The differences between the DDA and MSTM can be controlled to be less than 3% by using dipole size much smaller than the monomer size, and the DDA efficiency is sensitive to aggregate structures, e.g. lacy or compact. We find that shape representation for small-sized monomers during DDA discretization leads significant errors, i.e., up to 10%, and relatively large refractive index of BC also affects the DDA accuracy. However, the MSTM treats the BC monomers as perfect spheres without overlapping, and the imperfect structure that is implicitly introduced in the DDA simulations due to the spatial discretization may be a better representation of realistic BC particles. Moreover, the accuracy and efficiency of the DDA can be improved by defining dipoles on the particle boundary to have refractive indices given by the effective medium approximation (EMA). This leads to the adequate shape representation even using larger dipole sizes, and results in the DDA accuracy comparable to that of the reference MSTM solution.

KW - Black carbon aggregate

KW - Discrete-dipole approximation

KW - Effective medium approximation

KW - T-MATRIX

KW - RADIATIVE PROPERTIES

KW - LIGHT-SCATTERING

KW - PARAMETERS

KW - SOOT AEROSOLS

KW - ICE CRYSTALS

KW - DIFFERENCE TIME-DOMAIN

KW - CONVERGENCE

KW - ABSORPTION

KW - MORPHOLOGY

UR - http://www.scopus.com/inward/record.url?scp=85054425678&partnerID=8YFLogxK

U2 - 10.1016/j.jqsrt.2018.09.030

DO - 10.1016/j.jqsrt.2018.09.030

M3 - Article

AN - SCOPUS:85054425678

VL - 221

SP - 98

EP - 109

JO - Journal of Quantitative Spectroscopy and Radiative Transfer

JF - Journal of Quantitative Spectroscopy and Radiative Transfer

SN - 0022-4073

ER -