State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, and Center for Environment and Health, Peking University, Beijing 100871, People's Republic of China.
State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, and Center for Environment and Health, Peking University, Beijing 100871, People's Republic of China.
J Hazard Mater. 2021 Jul 5;413:125406. doi: 10.1016/j.jhazmat.2021.125406. Epub 2021 Feb 11.
The evolution of brown carbon (BrC) during atmospheric aging, including the changes in optical properties and chemical compositions, is still unclear. Light absorption and fluorescence of BrC fraction extracted from fresh and ozonized propane soot particles by methanol were systematically measured, which showed that (1) the mass absorption efficiencies (MAE) sharply decreased by ozone (O) aging (e.g., 1.2 ± 0.3-0.8 ± 0.1 m g for MAE), but changed slowly with increased O concentration (e.g., from 0.7 ± 0.2-0.8 ± 0.1 m g for MAE); (2) the fluorescence emission peaks were blue shifted, implying a loss of conjugated structures; (3) excitation-emission matrix analysis suggested that humic-like substances, charge transfer complexes, and polycyclic aromatic hydrocarbon (PAH)-like substances were the main chromophores. The PAH loss, accompanied by the decline of surface C˭C content, contributed more to the change of optical properties than the oxygenated PAH formation, thereby leading to the decrease in light absorption and fluorescence with O aging. This research reveals the importance of identifying the components responsible for optical properties in investigating the evolution of BrC during atmospheric aging, and is benefit for improving the evaluation of BrC's radiative forcing.
棕色碳（BrC）在大气老化过程中的演变，包括光学性质和化学成分的变化，仍然不清楚。本研究系统地测量了甲醇从新鲜和臭氧丙烷 soot 颗粒中提取的 BrC 馏分的光吸收和荧光，结果表明：（1）臭氧（O）老化（例如，1.2±0.3-0.8±0.1 m g 质量吸收效率（MAE））会导致 MAE 急剧降低，但随着 O 浓度的增加，MAE 的变化很慢（例如，从 0.7±0.2-0.8±0.1 m g 增加）；（2）荧光发射峰发生蓝移，表明共轭结构的损失；（3）激发-发射矩阵分析表明，腐殖质类物质、电荷转移复合物和多环芳烃（PAH）类物质是主要的发色团。与含氧 PAH 形成相比，PAH 的损失伴随着表面 C˭C 含量的下降，对光学性质的变化贡献更大，从而导致 O 老化时光吸收和荧光的下降。这项研究揭示了在研究大气老化过程中 BrC 演变时，确定对光学性质负责的成分的重要性，这有利于提高对 BrC 辐射强迫的评估。
