Institute of Physical Chemistry Polish Academy of Sciences, 01-224 Warsaw, Poland.
Atmospheric Chemistry Department (ACD), Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany.
Sci Total Environ. 2023 Jun 25;879:162622. doi: 10.1016/j.scitotenv.2023.162622. Epub 2023 Mar 5.
C- and C- unsaturated oxygenated organic compounds emitted by plants under stress like cutting, freezing or drying, known as Green Leaf Volatiles (GLVs), may clear some of the existing uncertainties in secondary organic aerosol (SOA) budget. The transformations of GLVs are a potential source of SOA components through photo-oxidation processes occurring in the atmospheric aqueous phase. Here, we investigated the aqueous photo-oxidation products from three abundant GLVs (1-penten-3-ol, (Z)-2-hexen-1-ol, and (E)-2-hexen-1-al) induced by OH radicals, carried out in a photo-reactor under simulated solar conditions. The aqueous reaction samples were analyzed using advanced hyphenated mass spectrometry techniques: capillary gas chromatography mass spectrometry (c-GC-MS); and reversed-phase liquid chromatography high resolution mass spectrometry (LC-HRMS). Using carbonyl-targeted c-GC-MS analysis, we confirmed the presence of propionaldehyde, butyraldehyde, 1-penten-3-one, and 2-hexen-1-al in the reaction samples. The LC-HRMS analysis confirmed the presence of a new carbonyl product with the molecular formula CHO, which probably bears the hydroxyhexenal or hydroxyhexenone structure. Density functional theory (DFT)-based quantum calculations were used to evaluate the experimental data and obtain insight into the formation mechanism and structures of the identified oxidation products via the addition and hydrogen-abstraction pathways. DFT calculations highlighted the importance of the hydrogen abstraction pathway leading to the new product CHO. Atmospheric relevance of the identified products was evaluated using a set of physical property data like Henry's law constant (HLC) and vapor pressure (VP). The unknown product of molecular formula CHO has higher HLC and lower VP than the parent GLV and thus has potential to remain in the aqueous phase leading to possible aqueous SOA formation. Other observed carbonyl products are likely first stage oxidation products and precursors of aged SOA.
植物在受到切割、冷冻或干燥等压力时会排放出 C- 和 C- 不饱和含氧有机化合物，称为绿叶挥发物 (GLVs)，它们可能会消除二次有机气溶胶 (SOA) 预算中一些现有的不确定性。GLVs 的转化是通过大气水相中的光氧化过程形成 SOA 成分的潜在来源。在这里，我们研究了在模拟太阳条件下的光反应器中，由 OH 自由基引发的三种丰富的 GLVs（1-戊烯-3-醇、（Z）-2-己烯-1-醇和（E）-2-己烯-1-醛）的水相光氧化产物。使用先进的串联质谱技术分析水相反应样品：毛细管气相色谱质谱联用仪 (c-GC-MS)；和反相液相色谱高分辨率质谱 (LC-HRMS)。使用羰基靶向 c-GC-MS 分析，我们在反应样品中确认了丙醛、丁醛、1-戊烯-3-酮和 2-己烯-1-醛的存在。LC-HRMS 分析证实了具有分子式 CHO 的新羰基产物的存在，该产物可能具有羟基己烯醛或羟基己烯酮结构。基于密度泛函理论 (DFT) 的量子计算用于评估实验数据，并通过加成和氢提取途径获得对所鉴定氧化产物形成机制和结构的深入了解。DFT 计算强调了导致新产物 CHO 的氢提取途径的重要性。通过一组物理性质数据，如亨利定律常数 (HLC) 和蒸气压 (VP)，评估了所鉴定产物的大气相关性。具有未知分子式 CHO 的未知产物具有比母体 GLV 更高的 HLC 和更低的 VP，因此有可能保留在水相中，从而可能形成水相 SOA。其他观察到的羰基产物可能是第一阶段氧化产物和老化 SOA 的前体。
