Black carbon (BC) exerts profound impacts on air quality and climate because of its high-absorption cross section over a broad band of solar spectrum. Non-BC materials coated on BC could alter the mixing state of BC particles and can considerably enhance its mass absorption coefficient. Quantification of this absorption enhancement remains a challenge due to incomplete understanding of the complex physical and chemical properties related to mixing states. In this paper, we summarize the recent progress in measurement and modeling studies on the BC mixing state and their effects on optical properties. Laboratory and field-based observations have shown that the transformation of a mixing state from a highly fractal nature to a more compact shape exhibits a decrease in electric mobility diameter but an increase in fractal dimension and effective density. Meanwhile, the transition behavior is also obviously influenced by emission source which can determine the components of BC mixtures. Based on the empirically determined parameters, accurate numerical modeling shows great capability on calculating BC optical properties. However, considering the significant uncertainties related to BC microphysical properties, proper parameterization considering realistic BC aggregates and coating fraction can help to understand the progress from an externally to internally mixed state.

由于黑碳（BC）在宽广的太阳光谱带中具有高吸收截面，因此对空气质量和气候产生深远影响。涂覆在BC上的非BC材料可以改变BC颗粒的混合状态，并可以大大提高其质量吸收系数。由于对与混合状态有关的复杂物理和化学性质的不完全了解，这种吸收增强的定量仍然是一个挑战。在本文中，我们总结了有关BC混合态及其对光学性能的影响的测量和建模研究的最新进展。实验室和基于现场的观察结果表明，混合态从高分形性质到更紧凑的形状的转变表现出电迁移率直径的减小，但分形维数和有效密度的增加。同时，过渡行为也受到排放源的明显影响，可以确定BC混合物的成分。基于经验确定的参数，精确的数值模型显示出计算BC光学特性的强大能力。但是，考虑到与BC微物理特性有关的重大不确定性，考虑实际BC聚集体和涂层分数的适当参数设置可以帮助了解从外部混合状态到内部混合状态的进展。过渡行为也受到排放源的明显影响，该排放源可以确定BC混合物的成分。基于经验确定的参数，精确的数值建模显示出计算BC光学特性的强大能力。但是，考虑到与BC微物理特性有关的重大不确定性，考虑实际BC聚集体和涂层分数的适当参数设置可以帮助理解从外部混合状态到内部混合状态的进展。过渡行为也受到排放源的明显影响，该排放源可以确定BC混合物的成分。基于经验确定的参数，精确的数值建模显示出计算BC光学特性的强大能力。但是，考虑到与BC微物理特性有关的重大不确定性，考虑实际BC聚集体和涂层分数的适当参数设置可以帮助了解从外部混合状态到内部混合状态的进展。