Abstract The magnitude of radiative forcing by soot is strongly dependent on its morphology and mixing state, which continuously evolve during atmospheric aging. One of the major soot aging mechanisms is via interaction with condensable trace-gas chemicals, and our previous study has shown the formation of two distinct coating distributions on fractal soot aggregates, primarily depending on the radius of monomer spheres and supersaturation of the condensing vapor. The two coating distributions, spherical shells around monomers and pendular rings in junctions between monomers, differ profoundly in their ability to restructure soot aggregates. Here, we investigate the impact of these two distributions on the optical properties of soot, using Discrete Dipole Approximation (DDA) calculations, which are also compared against the Rayleigh Debye Gans (RDG) approximation and the core-shell model. For most optical parameters, the difference between the two coating distributions was minor, except for the asymmetry parameter, where it was significant (5–13%). We found that the placement of condensate in junctions significantly depressed the asymmetry parameter for most coating volumes, thus promoting isotropic scattering by soot. Compared to a uniform condensate distribution, the presence of coating between monomers always resulted in slightly larger absorption, scattering and single scattering albedo (SSA), with the difference reaching ~10% for scattering at high coating volumes. We found that the RDG approximation underestimated absorption, but was able to predict scattering to within ~3%. On the other hand, the core-shell model significantly overestimated absorption, scattering, and SSA, especially for thinly coated soot.

中文翻译：

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具有均匀和摆动环涂层的烟灰聚集体对光的吸收和散射

摘要 烟尘辐射强迫的大小很大程度上取决于烟尘的形态和混合状态，它们在大气老化过程中不断演变。主要的烟灰老化机制之一是通过与可冷凝痕量气体化学品的相互作用，我们之前的研究表明，在分形烟灰聚集体上形成两种不同的涂层分布，主要取决于单体球体的半径和冷凝蒸汽的过饱和度。两种涂层分布，单体周围的球壳和单体之间连接处的钟摆环，在重组烟灰聚集体的能力方面存在很大差异。在这里，我们使用离散偶极近似 (DDA) 计算来研究这两种分布对烟尘光学特性的影响，它们还与瑞利德拜甘斯 (RDG) 近似和核壳模型进行了比较。对于大多数光学参数，两种涂层分布之间的差异很小，但不对称参数除外，该参数非常显着（5-13%）。我们发现冷凝物在结点中的放置显着降低了大多数涂层体积的不对称参数，从而促进了烟灰的各向同性散射。与均匀的冷凝物分布相比，单体之间涂层的存在总是导致稍大的吸收、散射和单散射反照率 (SSA)，对于高涂层体积的散射，差异达到约 10%。我们发现 RDG 近似低估了吸收，但能够将散射预测到约 3% 以内。另一方面，