Black carbon (BC) aerosols exert important effects on regional and global climate, whilst there still are significant uncertainties in their optical properties, particularly the spectral varying Angstrom exponents. This study numerically evaluates the influences of coating morphologies on optical properties of BC with non-absorbing coating, and evaluates the sensitivity of their Angstrom exponents, including extinction Angstrom exponent (EAE), absorption Angstrom exponent (AAE) and single scattering albedo Angstrom exponent (SSAAE), to particle microphysics with the multiple-sphere T-matrix method. Among all microphysical parameters, the shell/core ratio and size distribution play substantial roles in determining the EAE, AAE and SSAAE of coated BC, wherein the dependences of the Angstrom exponents on size distribution are higher. The EAE, AAE and SSAAE of coated BC by non-absorptive materials with different particle size distributions change in ranges of 0.3–1.5, 0.3–2.5 and –0.1–0.9, respectively. The core-shell Mie model can hardly produce accurate results of the Angstrom exponents of coated BC particles, especially the AAE and SSAAE. Our study reveals that BC coated by non-absorbing materials with large size distribution of coated BC may show negative SSAAE values for some coating microphysics, indicating the limitation of separating brown carbon from black carbon with a criterion of negative SSAAE.

黑碳（BC）气溶胶对区域和全球气候都具有重要影响，而它们的光学特性（尤其是光谱变化的埃斯特朗斯指数）仍存在很大的不确定性。本研究从数值上评估了涂层形态对非吸收涂层BC光学性能的影响，并评估了其Angstrom指数的灵敏度，包括消光Angstrom指数（EAE），吸收Angstrom指数（AAE）和单散射反照率Angstrom指数（ SSAAE），以多球体T-矩阵方法进行粒子微物理学。在所有微物理参数中，壳/核比和尺寸分布在确定包被的BC的EAE，AAE和SSAAE方面起着重要作用，其中埃斯特罗姆指数对尺寸分布的依赖性更高。EAE，不同粒径分布的非吸收性材料包被的BC的AAE和SSAAE的变化范围分别为0.3–1.5、0.3–2.5和–0.1–0.9。核-壳Mie模型几乎无法得出包衣的BC颗粒（尤其是AAE和SSAAE）的埃指数的准确结果。我们的研究表明，对于某些涂层微观物理学而言，由具有较大分布的涂层BC的非吸收性材料涂层的BC可能显示负SSAAE值，这表明以负SSAAE为标准将褐碳与黑碳分离的局限性。特别是AAE和SSAAE。我们的研究表明，对于某些涂层微观物理学而言，由具有较大分布的涂层BC的非吸收性材料涂层的BC可能显示负SSAAE值，这表明以负SSAAE为标准将褐碳与黑碳分离的局限性。特别是AAE和SSAAE。我们的研究表明，对于某些涂层微观物理学而言，由具有较大分布的涂层BC的非吸收性材料涂层的BC可能显示负SSAAE值，这表明以负SSAAE为标准将褐碳与黑碳分离的局限性。