Simplifying the calculation of light scattering properties for black carbon fractal aggregates
Simplifying the calculation of light scattering properties for black carbon fractal aggregates
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DOI：
10.5194/acp-14-7825-2014
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发表时间：
2014-08
影响因子：
6.3
通讯作者：
Andrew J A C Smith;R. Grainger
中科院分区：
文献类型：
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作者：
Andrew J A C Smith;R. Grainger
黑碳分形聚集体具有复杂的形状，使得计算其光学性质的计算成本特别高。本文提出了一种通过将简化模型优化为全光散射计算来估计分形聚集体光散射特性的方法。研究发现，在可见光或近热红外中，没有任何可能的球形模型（在任何尺寸或折射率下）可以很好地表示光散射。因此，当严格散射计算的大量计算开销无法证明时，将光散射参数化为聚集粒子数量的函数是模拟黑碳分布最实用的选择。该参数可以解析集成，以提供黑碳分形聚集体的对数正态分布的光散射特性，并以0.1%的ac精度返回典型黑碳粒径分布的消光截面。得到的散射截面和不对称参数在3%以内。
Black carbon fractal aggregates have complicated shapes that make the calculation of their optical properties particularly computationally expensive. Here, a method is presented to estimate fractal aggregate light scattering prop- erties by optimising simplified models to full light scattering calculations. It is found that there are no possible spherical models (at any size or refractive index) that well represent the light scattering in the visible or near-thermal infrared. As such, parameterisations of the light scattering as a func- tion of the number of aggregate particles is presented as the most pragmatic choice for modelling distributions of black carbon when the large computational overheads of rigorous scattering calculations cannot be justified. This parameterisa- tion can be analytically integrated to provide light scattering properties for lognormal distributions of black carbon fractal aggregates and return extinction cross sections with 0.1 % ac- curacy for typical black carbon size distributions. Scattering cross sections and the asymmetry parameter can be obtained to within 3 %.