Abstract Biomass burning (BB) is an important source of brown carbon (BrC) in atmospheric aerosols. The aim of this study is to investigate the light absorbing ability and oxidative potential of BB-derived BrC fractions (including not only the water soluble fraction but the water-insoluble ones). For this purpose, BrC fractions in the smoke particles (PM2.5) generated from burning of crop residues (rice straw, wheat straw, and corn straw) and wood stems (pine wood and Chinese fir) were sequentially extracted and fractionated into water- and alkaline-soluble extracts, and water- and alkaline-soluble humic-like substances (HULISWS and HULISAS). Their organic carbon (OC) contents, light absorption, and oxidative potential were comparably investigated. The results showed that the OC within water extracts (WSOC) and alkaline extracts (ASOC), and HULISWS and HULISAS accounted for 24.8%–28.5%, 10.7%–15.3%, 12.4%–16.6%, and 2.2%–5.6% of the BB smoke PM2.5 mass, respectively, thereby indicating that BB potentially influenced the atmospheric water-soluble and alkaline-soluble BrC levels. The BrC fractions had similar absorption patterns, but they also exhibited distinct features. BrC SUVA254 decreased in the order of: HULISAS (3.68–4.58 m2/gC) > HULISWS (2.99–3.72 m2/gC) > WSOC (2.54–2.80 m2/gC) > ASOC (1.30–2.06 m2/gC). BrC MAE365 was in the order of: HULISAS (1.95–2.40 m2/gC) > HULISWS (1.12–1.60 m2/gC) > WSOC (0.86–1.23 m2/gC) and ASOC (0.54–0.95 m2/gC). These results suggest that the HULIS fractions exhibited high aromaticity and strong light absorption. Moreover, BB extractable fractions exhibited a strong oxidative potential to generate reactive oxygen species, and the dithiothreitol activity followed the order of: water extracts (12.5–20.6 pmol/min/μg) > alkaline extracts (9.3–16.2 pmol/min/μg) > HULISWS (6.6–10.7 pmol/min/μg) > HULISAS (3.7–7.1 pmol/min/μg). The chemical characteristics of the BB BrC fractions also varied among the biomass types, where the crop residue smoke PM2.5 contained more BrC than wood smoke PM2.5, but the water-soluble BrC in the former generally exhibited weaker light absorption than the latter.

中文翻译：

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实验室模拟生物质燃烧产生的烟雾颗粒中水溶性和碱溶性褐碳的光学性质和氧化势

摘要 生物质燃烧（BB）是大气气溶胶中褐碳（BrC）的重要来源。本研究的目的是研究 BB 衍生的 BrC 部分（不仅包括水溶性部分，还包括水不溶性部分）的光吸收能力和氧化潜力。为此，燃烧农作物秸秆（稻草、麦秆和玉米秸秆）和木茎（松木和杉木）产生的烟雾颗粒 (PM2.5) 中的 BrC 部分被依次提取并分馏成水-和碱溶性提取物，以及水溶性和碱溶性腐殖质类物质（HULISWS 和 HULISAS）。对它们的有机碳 (OC) 含量、光吸收和氧化电位进行了比较研究。结果表明，水提物（WSOC）和碱性提取物（ASOC）中的OC，HULISWS 和 HULISAS 分别占 BB 烟雾 PM2.5 质量的 24.8%–28.5%、10.7%–15.3%、12.4%–16.6% 和 2.2%–5.6%，从而表明 BB 可能影响大气水-可溶性和碱溶性 BrC 水平。BrC 馏分具有相似的吸收模式，但它们也表现出不同的特征。BrC SUVA254 按以下顺序下降：HULISAS (3.68–4.58 m2/gC) > HULISWS (2.99–3.72 m2/gC) > WSOC (2.54–2.80 m2/gC) > ASOC (1.30–2.06 m2/gC)。BrC MAE365 的顺序为：HULISAS (1.95–2.40 m2/gC) > HULISWS (1.12–1.60 m2/gC) > WSOC (0.86–1.23 m2/gC) 和 ASOC (0.54–0.95 m2/gC)。这些结果表明 HULIS 馏分表现出高芳香性和强光吸收。此外，BB 可提取部分表现出很强的氧化潜力，可以产生活性氧，并且二硫苏糖醇活性遵循以下顺序：水提取物 (12.5–20.6 pmol/min/μg) > 碱性提取物 (9.3–16.2 pmol/min/μg) > HULISWS (6.6–10.7 pmol/min/μg) > HULISAS (3.7 –7.1 pmol/min/μg）。BB BrC 组分的化学特征也因生物质类型而异，其中作物残留烟雾 PM2.5 比木烟 PM2.5 含有更多 BrC，但前者中的水溶性 BrC 通常表现出比后者弱的光吸收.