Organic peroxy radical chemistry in oxidation flow reactors and environmental chambers and their atmospheric relevance
Organic peroxy radical chemistry in oxidation flow reactors and environmental chambers and their atmospheric relevance
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DOI：
10.5194/acp-19-813-2019
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发表时间：
2019-01-22
影响因子：
6.3
通讯作者：
Jimenez, Jose L.
中科院分区：
文献类型：
--
作者：
Peng, Zhe;Lee-Taylor, Julia;Jimenez, Jose L.
氧化流动反应器(OFR)是研究大气氧化过程和二次气溶胶形成的环境小室的一个很有前途的补充。然而，人们对OFRS内的化学物质与对流层中的化学物质有多大的代表性提出了疑问。我们通过化学动力学模型研究了在大气有机化学中起核心作用的有机过氧基团(RO2)在OFR和环境舱中的命运，并与各种环境条件进行比较，以帮助定义一系列与大气相关的OFR操作条件。对于大多数类型的RO2，它们在OFRs中的双分子命运主要是RO2+HO2和RO2+NO，类似于小室和大气研究。对于被取代的原生RO2和酰基RO2，RO2+RO2对RO2在OFRs、反应室和大气中的去向有很大的贡献，但OFRs中的RO2+RO2总体上没有大气中的RO2那么重要。在高NO时，RO2+NO在OFRs中主导RO2的去向，就像在大气中一样。在OFRS的高紫外灯设置下，RO2+OH可能是主要的RO2归宿，对于常见的多功能RO2来说，RO2的异构化可以忽略不计，这两者都偏离了常见的大气条件。在OFR254操作模式下(在这种模式下，只有添加的O-3才能通过光解生成OH)，我们找不到任何条件可以同时避免在254 nm处显著的有机光解，并导致足够长的RO2寿命(类似于10 S)，从而允许与大气相关的RO2异构化。在OFR185模式(由185 nm光子引发的反应生成OH)中，稳定物种和RO2的大气相关气相化学需要高相对湿度、低紫外光强度和低前体浓度。这些条件确保了RO2+OH的微小或可以忽略不计，以及RO2异构化在OFRs中RO2归宿中的相对重要性，其范围与大气中的x2相似。在这些条件下，OFR185系统内的光化学年龄最多可达到相当于几天的时间，包括最大二次有机气溶胶(SOA)产生的典型年龄。OFR温度的小幅升高可能会使RO2异构化的相对重要性接近环境值。为了研究在大气相关的OFR条件下形成的SOA的非均相氧化，需要在SOA形成阶段之后使用不同的更高强度的紫外源，这可以用另一个串联的反应器来完成。最后，我们建议通过报告在所有箱式和流动反应器实验中测量和/或估计的OH、HO2、NO、NO2和OH的反应性(或至少是前体成分和浓度)来评估RO2化学的大气相关性。本文还包括了一个简单易用的RO2归宿估算程序，以便于在未来的研究中对这一课题进行研究。
Oxidation flow reactors (OFRs) are a promising complement to environmental chambers for investigating atmospheric oxidation processes and secondary aerosol formation. However, questions have been raised about how representative the chemistry within OFRs is of that in the troposphere. We investigate the fates of organic peroxy radicals (RO2), which play a central role in atmospheric organic chemistry, in OFRs and environmental chambers by chemical kinetic modeling and compare to a variety of ambient conditions to help define a range of atmospherically relevant OFR operating conditions. For most types of RO2, their bimolecular fates in OFRs are mainly RO2 + HO2 and RO2 + NO, similar to chambers and atmospheric studies. For substituted primary RO2 and acyl RO2, RO2 + RO2 can make a significant contribution to the fate of RO2 in OFRs, chambers and the atmosphere, but RO2 + RO2 in OFRs is in general somewhat less important than in the atmosphere. At high NO, RO2 + NO dominates RO2 fate in OFRs, as in the atmosphere. At a high UV lamp setting in OFRs, RO2 + OH can be a major RO2 fate and RO2 isomerization can be negligible for common multifunctional RO2, both of which deviate from common atmospheric conditions. In the OFR254 operation mode (for which OH is generated only from the photolysis of added O-3), we cannot identify any conditions that can simultaneously avoid significant organic photolysis at 254 nm and lead to RO2 lifetimes long enough (similar to 10 s) to allow atmospherically relevant RO2 isomerization. In the OFR185 mode (for which OH is generated from reactions initiated by 185 nm photons), high relative humidity, low UV intensity and low precursor concentrations are recom-mended for the atmospherically relevant gas-phase chemistry of both stable species and RO2. These conditions ensure minor or negligible RO2 + OH and a relative importance of RO2 isomerization in RO2 fate in OFRs within similar to x2 of that in the atmosphere. Under these conditions, the photochemical age within OFR185 systems can reach a few equivalent days at most, encompassing the typical ages for maximum secondary organic aerosol (SOA) production. A small increase in OFR temperature may allow the relative importance of RO2 isomerization to approach the ambient values. To study the heterogeneous oxidation of SOA formed under atmospherically relevant OFR conditions, a different UV source with higher intensity is needed after the SOA formation stage, which can be done with another reactor in series. Finally, we recommend evaluating the atmospheric relevance of RO2 chemistry by always reporting measured and/or estimated OH, HO2, NO, NO2 and OH reactivity (or at least precursor composition and concentration) in all chamber and flow reactor experiments. An easy-to-use RO2 fate estimator program is included with this paper to facilitate the investigation of this topic in future studies.