Evaluation of the chemical composition of gas- and particle-phase products of aromatic oxidation
Evaluation of the chemical composition of gas- and particle-phase products of aromatic oxidation
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DOI：
10.5194/acp-2020-161
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发表时间：
2020-03
影响因子：
6.3
通讯作者：
Archit Mehra;Yuwei Wang;J. Krechmer;A. Lambe;Francesca Majluf;M. Morris;M. Priestley;T. Bannan-T.-Bann
中科院分区：
文献类型：
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作者：
Archit Mehra;Yuwei Wang;J. Krechmer;A. Lambe;Francesca Majluf;M. Morris;M. Priestley;T. Bannan-T.-Bann
抽象的。芳香族挥发性有机化合物（VOCs）是人类排放到大气中的主要污染物，对城市地区臭氧和二次有机气溶胶（SOA）的形成都很重要。最近的研究表明，芳烃可能遵循以前未知的氧化化学途径，包括可导致形成高度氧化产物的自氧化。在这项研究中，我们评估的气相和颗粒相离子测量的羟基自由基氧化过程中取代的C9-芳香族异构体（1，3，5-三甲基苯，1，2，4-三甲基苯，丙基苯和异丙基苯）和取代的多环芳烃（1-甲基萘）在低和中等NOx的条件下。具有碘化物阴离子电离的飞行时间化学电离质谱仪（ToF-CIMS）与气体和气溶胶的过滤器入口（FIGAERO）一起用于检测颗粒相中的产物，而Vocus质子转移反应质谱仪（Vocus-PTR-MS）用于检测气相中的产物。在质谱中观察到的产物离子的信号进行了比较，为不同的前体和实验条件。在气相和颗粒相中的大部分质谱产物信号来自所有前体共有的离子，尽管信号分布对于不同的VOC是不同的。气相和颗粒相的组成是彼此不同的。离子对应于包含在近明确的气相主化学机制（MCM版本3.3.1）的产品被用作目前的科学认识的基准，这些与观察结果的比较表明，MCM是缺少一系列的高度氧化的产品从其机制。在颗粒相中，来自所有前体的大部分产物信号来自开环离子，其中很大一部分比以前报道的氧化程度更高，并且已经经历了进一步的氧化以形成高度氧化的有机分子（HOM）。OH氧化的扰动下，增加NOx，HOM-离子信号的颗粒相信号的贡献仍然升高更多的取代芳香族前体。高达43%的产物信号来自包括HOM在内的保留环的离子;这对于更多取代的芳族化合物是最重要的。独特的产品是这些系统中的次要组分，并且许多主导离子具有与其他系统同时的离子式，突出了利用标记离子进行SOA的挑战。
Abstract. Aromatic volatile organic compounds (VOCs) are key anthropogenic pollutants emitted to the atmosphere and are important for both ozone and secondary organic aerosol (SOA) formation in urban areas. Recent studies have indicated that aromatic hydrocarbons may follow previously unknown oxidation chemistry pathways, including autoxidation that can lead to the formation of highly oxidised products. In this study we evaluate the gas- and particle-phase ions measured by online mass spectrometry during the hydroxyl radical oxidation of substituted C9-aromatic isomers (1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, propylbenzene and isopropylbenzene) and a substituted polyaromatic hydrocarbon (1-methylnaphthalene) under low- and medium-NOx conditions. A time-of-flight chemical ionisation mass spectrometer (ToF-CIMS) with iodide–anion ionisation was used with a filter inlet for gases and aerosols (FIGAERO) for the detection of products in the particle phase, while a Vocus proton-transfer-reaction mass spectrometer (Vocus-PTR-MS) was used for the detection of products in the gas phase. The signal of product ions observed in the mass spectra were compared for the different precursors and experimental conditions. The majority of mass spectral product signal in both the gas and particle phases comes from ions which are common to all precursors, though signal distributions are distinct for different VOCs. Gas- and particle-phase composition are distinct from one another. Ions corresponding to products contained in the near-explicit gas phase Master Chemical Mechanism (MCM version 3.3.1) are utilised as a benchmark of current scientific understanding, and a comparison of these with observations shows that the MCM is missing a range of highly oxidised products from its mechanism. In the particle phase, the bulk of the product signal from all precursors comes from ring scission ions, a large proportion of which are more oxidised than previously reported and have undergone further oxidation to form highly oxygenated organic molecules (HOMs). Under the perturbation of OH oxidation with increased NOx, the contribution of HOM-ion signals to the particle-phase signal remains elevated for more substituted aromatic precursors. Up to 43 % of product signal comes from ring-retaining ions including HOMs; this is most important for the more substituted aromatics. Unique products are a minor component in these systems, and many of the dominant ions have ion formulae concurrent with other systems, highlighting the challenges in utilising marker ions for SOA.