Sunlight-absorbing aerosols, e.g., black and brown carbon (BC and BrC), have a potentially large, but highly uncertain contribution to climate warming. The spectral dependence of the aerosol absorption in the visible and near-UV regime is almost universally well-described with a heuristic power law, where the exponent is termed the absorption Ångström exponent. However, the underlying physicochemical causes for this relation are unknown. Here, a model is presented that predicts the emergence of the power law spectral dependence and unifies the absorption behavior of BC and BrC. Building on the theory of light-absorption in amorphous materials, the interaction between multiple functional groups upon absorption is predicted to be a key feature for this broad spectral dependence. This aerosol amorphous absorption model is in agreement with recent empirical findings and provides a conceptual basis for the additional research needed to better constrain the optical properties of light-absorbing aerosols and their environmental impact.

中文翻译：

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气溶胶阳光吸收的光谱依赖性模型

吸收阳光的气溶胶，例如黑碳和棕碳（BC和BrC），对气候变暖的影响可能很大，但不确定性很高。气溶胶吸收在可见光和近紫外条件下的光谱依赖性几乎可以通过启发式幂定律得到很好的描述，其中该指数称为吸收Ångström指数。但是，这种关系的潜在物理化学原因尚不清楚。在这里，提出了一个模型，该模型可预测幂律频谱相关性的出现并统一BC和BrC的吸收行为。基于无定形材料中的光吸收理论，吸收后多个官能团之间的相互作用被预测为这种广泛光谱依赖性的关键特征。