Abstract This work performed a systematic investigation on the aqueous hydroxyl radical (OH) - induced photochemical oxidation of three modestly-soluble precursors from biomass combustion including 4-methylsyringol (DMP), eugenol (Eug), and 2,4,6-trimethylphenol (TRMP) under both simulated sunlight and ultraviolet (UV) light irradiations. An Aerodyne soot particle aerosol mass spectrometer (SP-AMS) was used to monitor the bulk chemical and elemental compositions of aqueous secondary organic aerosol (aqSOA) formed. AqSOA mass yields varied in ranges of 80–190% and 0–200% under sunlight and UV light conditions, respectively. AqSOA oxygen-to-carbon (O/C) ratio and carbon oxidation state increased steadily under sunlight + OH condition, but increased then decreased under UV + OH condition. Organic acids including malic acid, glycolic acid, formic acid and oxalic acid were formed, and their total accounted for ~12% of SOA mass. The UV–vis spectral change suggested formation of light-absorbing organics. Reaction pathways were proposed by combining gas chromatography-mass spectrometry (GC-MS) and SP-AMS results. Under sunlight + OH condition, oligomerization, functionalization, and fragmentation processes all involved in aqSOA evolution, with more contribution from functionalization via hydroxylation and oxygenation reactions. Reaction mechanism of UV + OH oxidation was initially dominated by functionalization then by fragmentation, indicating by the decrease of total organic carbon (TOC) contents, formation of small organic acids and low-molecular-weight products. Our work highlights that combination of SP-AMS with GC-MS is a powerful method for laboratory investigation of aqueous-phase reactions.

中文翻译：

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羟基自由基对三种酚类化合物的水相氧化：深入了解二次有机气溶胶的形成产率、机制、产物和光学性质

摘要 这项工作对水羟基自由基 (OH) 诱导的生物质燃烧产生的三种中等可溶性前体的光化学氧化进行了系统研究，包括 4-甲基丁香酚 (DMP)、丁子香酚 (Eug) 和 2,4,6-三甲基苯酚。 TRMP) 在模拟阳光和紫外线 (UV) 光照射下。Aerodyne 烟尘颗粒气溶胶质谱仪 (SP-AMS) 用于监测形成的含水二次有机气溶胶 (aqSOA) 的整体化学和元素组成。在阳光和紫外线条件下，AqSOA 的质量产率分别在 80-190% 和 0-200% 的范围内变化。AqSOA氧碳(O/C)比和碳氧化态在阳光+OH条件下稳定增加，但在UV+OH条件下先增加后下降。有机酸包括苹果酸、乙醇酸、形成了甲酸和草酸，它们的总量约占 SOA 质量的 12%。紫外-可见光谱变化表明形成了吸光有机物。通过结合气相色谱-质谱 (GC-MS) 和 SP-AMS 结果提出了反应途径。在阳光 + OH 条件下，低聚化、功能化和裂解过程都参与了 aqSOA 的演化，其中通过羟基化和氧化反应的功能化贡献更大。UV + OH 氧化的反应机制最初由功能化然后由碎片控制，表明总有机碳 (TOC) 含量降低，形成小有机酸和低分子量产物。