Evolution of OH reactivity in NO-free volatile organic compound photooxidation investigated by the fully explicit GECKO-A model
Evolution of OH reactivity in NO-free volatile organic compound photooxidation investigated by the fully explicit GECKO-A model
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DOI：
10.5194/acp-21-14649-2021
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发表时间：
2021-10
影响因子：
6.3
通讯作者：
Zhe Peng;J. Lee-Taylor;H. Stark;J. Orlando;B. Aumont;J. Jimenez
中科院分区：
文献类型：
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作者：
Zhe Peng;J. Lee-Taylor;H. Stark;J. Orlando;B. Aumont;J. Jimenez
抽象。OH反应性（OHR）是对大气中氧化能力的重要控制，但在许多环境中，如偏远，农村和城市大气中，以及在低NO条件下的实验室实验装置中，仍然受到很大的限制。为了更好地理解OHR，其在挥发性有机化合物（VOCs）氧化过程中的演变是需要更好地量化的一个主要方面。我们使用完全显式生成器的显式化学和动力学的有机物在大气中（GECKO-A）模型来研究的OHR演变的NO-自由光氧化的几种VOCs，包括癸烷（烷烃），间二甲苯（芳香族），异戊二烯（烯烃）。氧化逐渐产生更饱和和官能化的物质。总有机OHR（包括前体和产物，OHRVOC）首先对于癸烷（因为官能化增加OH速率系数）和间二甲苯（因为形成更多反应性氧化烯烃）增加。对于异戊二烯，C=C键消耗导致OHRVOC在第一主要饱和多官能产物（即，异戊二烯环氧二醇。在不同前体的氧化中的饱和多官能物种具有相似的每个C原子的平均OHRVOC。后一种氧化遵循不同前体的类似过程，涉及多官能物质的碎片化，最终将C1和C2片段氧化为CO2，导致每个C原子的OHRVOC的类似演变。在完全氧化成CO2的过程中，总OH消耗的上限大约是每个C原子三个。我们还探讨了激进的回收率的趋势。我们发现，大气和环境室之间的OHRVOC的演变，大气和氧化流动反应器（OFR）之间的差异，可以是实质性的，前者甚至更大，但这些差异往往小于前体之间。室中含氧VOC的聚四氟乙烯壁损失导致OHRVOC与大气条件的大偏差，特别是对于较大前体的氧化，其中多功能物质可能遭受大量壁损失，导致OHRVOC的显著低估。对于OFR，OHRVOC演变的偏差从大气的情况下，主要是由于显着的OHR贡献RO 2和缺乏有效的有机光解。前者可以通过降低OFR中的UV灯设置来避免，而后者被证明是非常难以避免的。然而，前者可能会大大抵消由于缺乏有效的有机光解而导致的多功能物种破碎化的减缓。
Abstract. OH reactivity (OHR) is an important control on the oxidative capacity in the atmosphere but remains poorly constrained in many environments, such as remote, rural, and urban atmospheres, as well as laboratory experiment setups under low-NO conditions. For an improved understanding of OHR, its evolution during oxidation of volatile organic compounds (VOCs) is a major aspect requiring better quantification. We use the fully explicit Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) model to study the OHR evolution in the NO-free photooxidation of several VOCs, including decane (an alkane), m-xylene (an aromatic), and isoprene (an alkene). Oxidation progressively produces more saturated and functionalized species. Total organic OHR (including precursor and products, OHRVOC) first increases for decane (as functionalization increases OH rate coefficients) and m-xylene (as much more reactive oxygenated alkenes are formed). For isoprene, C=C bond consumption leads to a rapid drop in OHRVOC before significant production of the first main saturated multifunctional product, i.e., isoprene epoxydiol. The saturated multifunctional species in the oxidation of different precursors have similar average OHRVOC per C atom. The latter oxidation follows a similar course for different precursors, involving fragmentation of multifunctional species to eventual oxidation of C1 and C2 fragments to CO2, leading to a similar evolution of OHRVOC per C atom. An upper limit of the total OH consumption during complete oxidation to CO2 is roughly three per C atom. We also explore the trends in radical recycling ratios. We show that differences in the evolution of OHRVOC between the atmosphere and an environmental chamber, and between the atmosphere and an oxidation flow reactor (OFR), can be substantial, with the former being even larger, but these differences are often smaller than between precursors. The Teflon wall losses of oxygenated VOCs in chambers result in large deviations of OHRVOC from atmospheric conditions, especially for the oxidation of larger precursors, where multifunctional species may suffer substantial wall losses, resulting in significant underestimation of OHRVOC. For OFR, the deviations of OHRVOC evolution from the atmospheric case are mainly due to significant OHR contribution from RO2 and lack of efficient organic photolysis. The former can be avoided by lowering the UV lamp setting in OFR, while the latter is shown to be very difficult to avoid. However, the former may significantly offset the slowdown in fragmentation of multifunctional species due to lack of efficient organic photolysis.