Abstract Crop straw combustion is a significant source for humic-like substances (HULIS) in fine particles (PM2.5), which have strong light absorption in the near ultraviolet and visible light region. In this study, the relative abundances, light absorption properties and fluorescence characteristics of HULIS produced by three crop straws (wheat, rice and corn straws) combusted under different moisture contents and stacking modes were comprehensively characterized. The results show that the moisture contents and stacking modes can affect the ratio of carbon content in HULIS to water-soluble organic carbon (HULIS-C/WSOC) and the ratio of HULIS to PM2.5 (HULIS/PM2.5). The absorption Angstrom exponent (AAE) and absorptivity ratios between 250 and 365 nm (E2/E3) for HULIS increased either under high moisture or stacking conditions for all three crop straws, while mass absorption efficiencies at 365 nm (MAE365) decreased under high moisture or stacking conditions. Four fluorescent components of HULIS were identified based on the characterization of the excitation-emission matrix combined with a parallel factor analysis model (EEM-PARAFAC): protein-like organic matter (C1 and C4), highly oxygenated humic-like substances (C3) and less-oxygenated humic-like substances (C2). A correlation analysis of the fluorescent components and light absorption indicators showed that the components C4, (C2, C3) and (C1, C2) determined the variations in the light absorption properties of HULIS derived from wheat, rice and corn straw burning, respectively. We also found that the flame burning of crop straw could reduce the contribution of light absorption to HULIS per unit mass of crop straw.

中文翻译：

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HULIS在不同含水率和堆放方式下农作物秸秆燃烧产生的初级颗粒物中的吸光特性

摘要 农作物秸秆燃烧是细颗粒 (PM2.5) 中类腐殖质物质 (HULIS) 的重要来源，其在近紫外和可见光区域具有强光吸收。本研究综合表征了三种农作物秸秆（小麦、水稻和玉米秸秆）在不同含水量和堆放方式下燃烧产生的 HULIS 的相对丰度、光吸收特性和荧光特性。结果表明，水分含量和堆积方式会影响 HULIS 中的碳含量与水溶性有机碳的比率（HULIS-C/WSOC）和 HULIS 与 PM2.5 的比率（HULIS/PM2.5）。HULIS 的吸收埃指数 (AAE) 和 250 和 365 nm (E2/E3) 之间的吸收率比在高水分或所有三种作物秸秆的堆叠条件下增加，而在 365 nm (MAE365) 处的质量吸收效率在高水分下降低或堆叠条件。基于激发-发射矩阵的表征结合平行因子分析模型 (EEM-PARAFAC)，鉴定了 HULIS 的四种荧光成分：类蛋白质有机物（C1 和 C4）、高氧类腐殖质物质（C3）和含氧量较低的腐殖质类物质 (C2)。荧光成分与吸光指标的相关性分析表明，成分C4、（C2、C3）和（C1、C2）决定了小麦HULIS光吸收特性的变化，分别燃烧水稻和玉米秸秆。我们还发现，农作物秸秆的火焰燃烧可以降低光吸收对单位质量农作物秸秆 HULIS 的贡献。