Biomass burning (BB) and coal combustion (CC) are important sources of brown carbon (BrC) in ambient aerosols. In this study, six biomass materials and five types of coal were combusted to generate fine smoke particles. The BrC fractions, including water-soluble organic carbon (WSOC), humic-like substance carbon (HULIS-C), and methanol-soluble organic carbon (MSOC), were subsequently fractionated, and their optical properties and chemical structures were then comprehensively investigated using UV–visible spectroscopy, proton nuclear magnetic resonance spectroscopy (¹H NMR), and fluorescence excitation–emission matrix (EEM) spectroscopy combined with parallel factor (PARAFAC) analysis. In addition, the oxidative potential (OP) of BB and CC BrC was measured with the dithiothreitol (DTT) method. The results showed that WSOC, HULIS-C, and MSOC accounted for 2.3 %–22 %, 0.5 %–10 %, and 6.4 %–73 % of the total mass of combustion-derived smoke PM_2.5, respectively, with MSOC extracting the highest concentrations of organic compounds. The MSOC fractions had the highest light absorption capacity (mass absorption efficiency at 365 nm (MAE₃₆₅): 1.0–2.7 m²/gC) for both BB and CC smoke, indicating that MSOC contained more of the strong light-absorbing components. Therefore, MSOC may represent the total BrC better than the water-soluble fractions. Some significant differences were observed between the BrC fractions emitted from BB and CC with more water-soluble BrC fractions with higher MAE₃₆₅ and lower absorption Ångström exponent values detected in smoke emitted from BB than from CC. EEM-PARAFAC identified four fluorophores: two protein-like, one humic-like, and one polyphenol-like fluorophores. The protein-like substances were the dominant components of WSOC (47 %–80 %), HULIS-C (44 %–87 %), and MSOC (42 %–70 %). The ¹H-NMR results suggested that BB BrC contained more oxygenated aliphatic functional groups ($\mathrm{H}-\mathrm{C}-\mathrm{O}$), whereas CC BrC contained more unsaturated fractions ($\mathrm{H}-\mathrm{C}-\mathrm{C}=$ and Ar−H). The DTT assays indicated that BB BrC generally had a stronger oxidative potential (DTT_m, 2.6–85 pmol/min/µg) than CC BrC (DTT_m, 0.4–11 pmol/min/µg), with MSOC having a stronger OP than WSOC and HULIS-C. In addition, HULIS-C contributed more than half of the DTT activity of WSOC (63.1 % ± 15.5 %), highlighting that HULIS was a major contributor of reactive oxygen species (ROS) production in WSOC. Furthermore, the principal component analysis and Pearson correlation coefficients indicated that highly oxygenated humic-like fluorophore C4 may be the important DTT active substances in BrC.

中文翻译：

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生物质材料和煤燃烧排放的水溶性和甲醇溶性有机化合物的化学成分、光学性质和氧化潜力

生物质燃烧 (BB) 和煤燃烧 (CC) 是环境气溶胶中褐碳 (BrC) 的重要来源。在这项研究中，六种生物质材料和五种煤被燃烧以产生细小的烟雾颗粒。BrC组分，包括水溶性有机碳（WSOC）、类腐殖质碳（HULIS-C）和甲醇可溶性有机碳（MSOC），随后被分馏，然后对其光学性质和化学结构进行了综合研究使用紫外-可见光谱、质子核磁共振光谱（¹H NMR）和荧光激发-发射矩阵（EEM）光谱结合平行因子（PARAFAC）分析。此外，BB 和 CC BrC 的氧化电位 (OP) 用二硫苏糖醇 (DTT) 方法测量。结果表明，WSOC、HULIS-C 和 MSOC 分别占燃烧产生的烟雾 PM _2.5总质量的 2.3 %–22 %、0.5 %–10 % 和 6.4 %–73 % ，其中 MSOC 提取了有机化合物的最高浓度。MSOC 级分具有最高的光吸收能力（365 nm 处的质量吸收效率 (MAE ₃₆₅ )：1.0–2.7 m ²/gC) 对于 BB 和 CC 烟雾，表明 MSOC 包含更多的强光吸收成分。因此，MSOC 可能比水溶性部分更好地代表总 BrC。在从 BB 和 CC 发出的 BrC 部分之间观察到一些显着差异，其中更多的水溶性 BrC 部分具有更高的 MAE ₃₆₅和在从 BB 发出的烟雾中检测到的比从 CC 发出的烟雾中检测到的吸收 Ångström 指数值更低。EEM-PARAFAC 确定了四种荧光团：两种蛋白质样荧光团、一种腐殖质样荧光团和一种多酚样荧光团。类蛋白质物质是 WSOC (47 %–80 %)、HULIS-C (44 %–87 %) 和 MSOC (42 %–70 %) 的主要成分。的 ¹建议，BB BRC含有更多的含氧脂族官能团H-NMR结果（$\mathrm{H}——\mathrm{C}——\mathrm{哦}$)，而 CC BrC 包含更多的不饱和部分 ($\mathrm{H}——\mathrm{C}——\mathrm{C}=$和Ar-H )。DTT 测定表明，BB BrC 通常具有比 CC BrC（DTT _m，0.4-11 pmol/min/ µg）更强的氧化潜力（DTT _m，2.6-85 pmol/min/ µg），MSOC 具有更强的OP 比 WSOC 和 HULIS-C。此外，HULIS-C 贡献了 WSOC 一半以上的 DTT 活性（63.1 %  ±  15.5 %），突出表明 HULIS 是 WSOC 中活性氧 (ROS) 产生的主要贡献者。此外，主成分分析和 Pearson 相关系数表明，高度氧化的类腐殖质荧光团 C4 可能是 BrC 中重要的 DTT 活性物质。