The positive radiative forcing of black carbon (BC) aerosol depends not only on the spatial and temporal distribution of BC but also its absorption efficiency. The mass absorption cross section (MAC) of BC is enhanced by atmospheric aging processes that increase particle size and non‐BC coating amounts (mixing state) of BC‐containing particles. However, the representation of MAC (or absorption enhancement) in current global aerosol models has a large uncertainty. This study used a global aerosol model that resolves particle size and mixing state to show that the MAC of anthropogenic BC has increased by 50% from preindustrial to present‐day conditions (from 5.6 to 8.6 m² g⁻¹) because faster present‐day aging processes increase the fraction of thickly coated BC particles, which have high absorption efficiency. This effect is apparent only when the model considers BC mixing state with sufficient resolution. The impact of this MAC enhancement on BC direct radiative forcing is estimated to be 0.051–0.086 W m⁻² globally (22–37% of anthropogenic BC direct radiative forcing, 0.23 W m⁻²) and exceeds 0.5 W m⁻² near‐source regions in East Asia. Sensitivity simulations show that BC direct radiative forcing and MAC are highly sensitive to non‐BC emissions, secondary aerosol formation, and aerosol size distribution and mixing state in emissions. We must therefore improve our understanding of these factors by further observations and reduce their discrepancies between models to achieve better estimates of BC absorption efficiency and radiative forcing.

中文翻译：

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工业前和当前条件下通过尺寸和混合状态解析的全球气溶胶模型模拟的黑碳吸收效率

黑碳（BC）气溶胶的正辐射强迫不仅取决于BC的时空分布，还取决于其吸收效率。大气老化过程会提高BC的质量吸收横截面（MAC），该过程会增加含BC的颗粒的粒径和非BC涂层量（混合状态）。但是，目前的全球气溶胶模型中MAC（或吸收增强）的表示具有很大的不确定性。这项研究使用了可解析粒径和混合状态的全球气溶胶模型，表明从工业化前到当今的条件下，人为BC的MAC增加了50％（从5.6到8.6 m ²  g ^-1），因为当今更快的老化过程会增加具有高吸收效率的厚涂层BC颗粒的比例。仅当模型考虑具有足够分辨率的BC混合状态时，此效果才明显。MAC增强对BC直接辐射强迫的影响估计全球范围为0.051-0.086 W m ^-2（人为BC直接辐射强迫的22-37 ％，0.23 W m ^-2），并且超过0.5 W m ^-2东亚的近源地区。灵敏度模拟显示，BC直接辐射强迫和MAC对非BC排放，二次气溶胶形成，气溶胶尺寸分布和排放中的混合状态高度敏感。因此，我们必须通过进一步的观察来增进对这些因素的理解，并减少它们在模型之间的差异，以更好地估计BC吸收效率和辐射强迫。