Low molecular weight dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls as ozonolysis products of isoprene: Implication for the gaseous-phase formation of secondary organic aerosols
Low molecular weight dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls as ozonolysis products of isoprene: Implication for the gaseous-phase formation of secondary organic aerosols
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DOI：
10.1016/j.scitotenv.2020.144472
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发表时间：
2021-01-18
影响因子：
9.8
通讯作者：
Hirokawa, Jun
中科院分区：
文献类型：
--
作者：
Bikkina, Srinivas;Kawamura, Kimitaka;Hirokawa, Jun
异戊二烯是森林冠层释放的主要生物源挥发性有机化合物，其氧化是有机气溶胶中主要物种草酸的潜在来源。我们在这里评估臭氧分解的异戊二烯在干燥的黑暗中作为草酸（C-2），丙二酸（C-3）和琥珀酸（C-4）的来源。我们发现，草酸和甲基乙二醛是主要产品在10分钟内的反应，其次是乙醛酸，丙二酸或琥珀酸添加。有趣的是，从早期反应（9-29分钟）的氧化产物的分子分布的特点是由甲基乙二醛的优势，其次是C-2，30分钟后成为占主导地位。异戊二烯衍生的二次有机气溶胶（SOA）显示出化学演变与反应时间的二羧酸的分子特征类似的环境气溶胶（C-2>C-3 >= C-4）。甲基乙二醛的碳基相对丰度随反应时间的延长而稳定下降（40%-> 30%），而C-2的碳基相对丰度随反应时间的延长而增加（15%-> 25%），但乙二醛的碳基相对丰度没有持续变化（6-10%）。这一发现意味着甲基乙二醛是比乙二醛更重要的草酸中间体。相比之下，较小的变异性和较低的浓度比其他中间体的草酸和乙醛酸表明，草酸添加物的形成在干燥条件下遵循不同的途径比在水相多相化学通常调用云/雾/大气沃茨。在这里，我们提出了新的反应方案，高水平的甲基乙二醛和草酸添加通过气相化学反应与臭氧和OH自由基，以更好地解释周围的SOA组合物。此外，C-2的相对丰度表现出小的变化，从1至8小时，这表明其稳定的字符对羟基自由基的氧化。(C)2021爱思唯尔有限公司版权所有。
Oxidation of isoprene, a major biogenic volatile organic compound emitted from forest canopies, is a potential source of oxalic acid; the dominant species in organic aerosols. We evaluated here ozonolysis of isoprene in dry darkness as a source of oxalic (C-2), malonic (C-3) and succinic (C-4) acids. We found that oxalic acid and methylglyoxal are dominant products within 10 min of reaction followed by glyoxylic, malonic or succinic adds. Interestingly, molecular distributions of oxidation products from early reactions (9-29 min) were characterized by the predominance of methylglyoxal followed by C-2, which became dominant after 30 min. The isoprene-derived secondary organic aerosols (SOAs) showed chemical evolution with reaction time towards the molecular characteristics of dicarboxylic acids similar to those of ambient aerosols (C-2>C-3 >= C-4). The carbon-based relative abundances of methylglyoxal decreased steadily (40%-> 30%), while those of C-2 increased with reaction time (15%-> 25%), but no such variations persisted for glyoxal (6-10%). This finding means that methylglyoxal is more important intermediate of oxalic acid than glyoxal. In contrast, smaller variability and lower concentrations of pyruvic and glyoxylic acids than other intermediates indicate that oxalic add formation under dry conditions follows a different pathway than in aqueous-phase heterogeneous chemistry usually invoked for cloud/fog/atmospheric waters. Here, we propose new reaction schemes for high levels of methylglyoxal and oxalic add via gas-phase chemical reactions with ozone and OH radicals to better interpret the ambient SOA composition. Furthermore, the relative abundances of C-2 exhibit small variability from 1 to 8 h, suggesting its stable character towards the oxidation by hydroxyl radicals. (C) 2021 Elsevier B.V. All rights reserved.