Aqueous Photochemistry of 2-Methyltetrol and Erythritol as Sources of Formic Acid and Acetic Acid in the Atmosphere
Aqueous Photochemistry of 2-Methyltetrol and Erythritol as Sources of Formic Acid and Acetic Acid in the Atmosphere
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DOI：
10.1021/acsearthspacechem.1c00107
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发表时间：
2021-06-02
影响因子：
3.4
通讯作者：
Nguyen, Tran B.
中科院分区：
文献类型：
--
作者：
Cope, James D.;Abellar, Karizza A.;Nguyen, Tran B.
在大气模式中，特别是在高生物影响的地区，大气甲酸（FA）和乙酸（AA）的混合比往往被低估。我们研究了水羟基自由基（OH）氧化的2-甲基四醇，二次有机气溶胶（SOAs）的最大组成部分之一，是由异戊二烯的氧化，并比较其化学非甲基化的C-4多元醇类似物，ESTA。利用H-1和C-13核磁共振谱和高效液相色谱-高分辨质谱联用技术研究了水溶液中2-甲基四醇（2-MT）+ OH和2-甲基四醇（E）+ OH反应的动力学和反应产物。我们发现，脂肪醇，如E和2-MT的水氧化，是小酸的强来源。几乎所有的2-MT转化为FA，AA和二氧化碳（CO2）下大气相关的OH暴露。抑制挥发性酸分配到气相中增加了所观察到的产率的挥发性产品在溶液中高达80%，定量的实验与低顶空。研究了2-MT + OH反应中pH值对FA和AA（或其羧酸盐）产率的影响。溶液pH值强烈影响FA和AA的浓度，通过其气水分配，总产量，和自由基诱导的脱羧反应。动力学模型充分再现的数据，但是，不同的反应机制需要为低和高pH值的化学。与E相比，在高pH下观察到2-MT的稳定反应中间体较少，与低pH相比，提供了对2-MT分解途径的深入了解。大量的生产产量和分配的FA和AA在水相光氧化的2-甲基四醇的基础上，水性老化的异戊二烯衍生的SOA可能有助于FA和AA排放到大气中，目前缺少的模型。
Atmospheric formic acid (FA) and acetic acid (AA) mixing ratios are often underestimated in atmospheric models, particularly over areas with high biogenic influence. We investigated the aqueous hydroxyl radical (OH) oxidation of 2-methyltetrol, one of the largest components of secondary organic aerosols (SOAs) that are produced from the oxidation of isoprene, and compare its chemistry to the non-methylated C-4 polyol analogue, erythritol. We studied the kinetics and reaction products of the aqueous 2-methyltetrol (2-MT) + OH and erythritol (E) + OH reactions using H-1 and C-13 nuclear magnetic resonance spectroscopy and high-performance liquid chromatography coupled with high-resolution mass spectrometry. We found that the aqueous oxidation of aliphatic alcohols, such as E and 2-MT, are strong sources of small acids. Nearly all 2-MT is converted to FA, AA, and carbon dioxide (CO2) under atmospherically relevant OH exposures. Suppression of volatile acid partitioning into the gas phase increased the observed yields of volatile products in solution by up to 80%, as quantified by experiments with low headspace. The influence of solution pH on the yields of FA and AA (or their carboxylates) was also investigated in the range of pH 2-9 for the 2-MT + OH reaction. Solution pH strongly influenced the concentrations of FA and AA via their gas-aqueous partitioning, gross production yields, and radical-induced decarboxylation reactions. The data are adequately reproduced with a kinetic model; however, different reaction mechanisms are needed for the low and high pH chemistries. Fewer stable reaction intermediates were observed for 2-MT compared to E and at high pH compared to low pH, providing insight into the decomposition pathways of 2-MT. On the basis of the substantial production yields and partitioning of FA and AA in the aqueous photooxidation of 2-methyltetrol, aqueous aging of isoprene-derived SOA may contribute to FA and AA emissions to the atmosphere that are currently missing from models.