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Organic peroxy radical chemistry in oxidation flow reactors and environmental chambers and their atmospheric relevance

机译：氧化流反应器和环境室中的有机过氧自由基化学及其与大气的关系

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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 (ROsub2/sub), 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 ROsub2/sub, their bimolecular fates in OFRs are mainly ROsub2/sub?+?HOsub2/sub and ROsub2/sub?+?NO, similar to chambers and atmospheric studies. For substituted primary ROsub2/sub and acyl ROsub2/sub, ROsub2/sub?+?ROsub2/sub can make a significant contribution to the fate of ROsub2/sub in OFRs, chambers and the atmosphere, but ROsub2/sub?+?ROsub2/sub in OFRs is in general somewhat less important than in the atmosphere. At high NO, ROsub2/sub?+?NO dominates ROsub2/sub fate in OFRs, as in the atmosphere. At a high UV lamp setting in OFRs, ROsub2/sub?+?OH can be a major ROsub2/sub fate and ROsub2/sub isomerization can be negligible for common multifunctional ROsub2/sub, both of which deviate from common atmospheric conditions. In the OFR254 operation mode (for which OH is generated only from the photolysis of added Osub3/sub), we cannot identify any conditions that can simultaneously avoid significant organic photolysis at 254 nm and lead to ROsub2/sub lifetimes long enough (?～ 10 s) to allow atmospherically relevant ROsub2/sub 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 recommended for the atmospherically relevant gas-phase chemistry of both stable species and ROsub2/sub. These conditions ensure minor or negligible ROsub2/sub?+?OH and a relative importance of ROsub2/sub isomerization in ROsub2/sub fate in OFRs within ～ ×?2 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 ROsub2/sub 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 ROsub2/sub chemistry by always reporting measured and/or estimated OH, HOsub2/sub, NO, NOsub2/sub and OH reactivity (or at least precursor composition and concentration) in all chamber and flow reactor experiments. An easy-to-use ROsub2/sub fate estimator program is included with this paper to facilitate the investigation of this topic in future studies.
机译：氧化流反应器（OFR）是用于研究大气氧化过程和二次气溶胶形成的环境室的有前途的补充。但是，已经提出了关于OFR中的化学在对流层中的代表性如何的问题。我们通过化学动力学模型研究了有机过氧自由基（RO 2 ）的命运，它们在大气有机化学中，在OFR和环境室中起着至关重要的作用，并与各种环境条件进行比较以帮助定义一系列与大气有关的OFR操作条件。对于大多数类型的RO 2 ，它们在OFR中的双分子命运主要是RO 2 ？+？HO 2 和RO 2 ？+？NO，类似于暗室和大气研究。对于取代的一级RO 2 和酰基RO 2 ，RO 2 ？+？RO 2 可以做出重大贡献与OFR，房间和大气中RO 2 的命运有关，但是OFR中RO 2 ？+？RO 2 的命运通常要少一些比在大气中重要。在高NO时，与大气中一样，RO 2 ？+？NO决定了OFR中RO 2 的命运。在OFR中设置高紫外线灯时，RO 2 ？+？OH可能是主要的RO 2 命运，而RO 2 的异构化作用可以忽略不计常见的多功能RO 2 都偏离了常见的大气条件。在OFR254操作模式下（仅通过添加的O 3 的光解产生OH），我们无法确定可以同时避免在254 nm处发生显着有机光解并导致RO 的任何条件。 2 的寿命足够长（？〜10 s）以允许与大气相关的RO 2 异构化。在OFR185模式下（由185 nm光子引发的反应生成OH），建议使用高相对湿度，低UV强度和低前体浓度，以用于与大气有关的稳定物质和RO 2的气相化学反应。这些条件确保了在OFR中RO 2 ？+？OH的微量或可忽略不计，以及RO 2 异构化的相对重要性在×内。 ？2在大气中。在这些条件下，OFR185系统内的​​光化学年龄最多可以达到几天，相当于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使RO 2 异构化的相对重要性接近环境值。为了研究在与大气有关的OFR条件下形成的SOA的异质氧化，在SOA形成阶段之后需要具有更高强度的不同UV源，这可以使用另一个串联的反应器完成。最后，我们建议通过始终报告测量和/或估算的OH，HO 2 ，NO，NO 2 来评估RO 2 化学物质与大气的相关性在所有反应室和流动反应器实验中，OH反应性（或至少是前体组成和浓度）。本文包含一个易于使用的RO 2 命运估计程序，以方便在将来的研究中对该主题进行调查。

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