Heterogeneous Oxidation of Atmospheric Organic Aerosol: Kinetics of Changes to the Amount and Oxidation State of Particle-Phase Organic Carbon
Heterogeneous Oxidation of Atmospheric Organic Aerosol: Kinetics of Changes to the Amount and Oxidation State of Particle-Phase Organic Carbon
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DOI：
10.1021/acs.jpca.5b06946
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发表时间：
2015-11-05
影响因子：
2.9
通讯作者：
Wilson, Kevin R.
中科院分区：
文献类型：
--
作者：
Kroll, Jesse H.;Lim, Christopher Y.;Wilson, Kevin R.
众所周知，大气氧化反应会在几天的时间尺度上影响有机气溶胶(OA)颗粒的化学成分，但这种氧化老化反应的细节却知之甚少。在这项研究中，我们考察了一类关键的老化反应的速率和产物，即气相羟基自由基(OH)对颗粒相有机物种的非均相氧化。我们汇编并重新分析了我们实验室以前的一些研究，这些研究涉及单组分有机颗粒的氧化。所有的动力学和产物数据都是在一个共同的基础上描述的，从而能够在不同的化学体系和实验条件之间进行直接的比较。氧化化学是根据OA的关键系综性质的变化来描述的，而不是其详细的分子组成，特别是关注两个量，即颗粒相碳的数量和氧化状态。非均相氧化增加了颗粒碳的氧化态，增加的速度由详细的化学机理决定。同时，颗粒相碳的数量随着氧化而减少，这是由于碎裂(C-C断裂)反应形成了逃逸到气相的小的挥发性产物。与氧化态的增加相比，大多数体系的碳损失速率几乎是一致的。将这些结果外推到大气条件表明，非均相氧化可以在几天的时间尺度上对大气中的有机酸的数量和组成产生重大影响，这一预测与对这种长时间尺度上的大气酸演变的现有测量大体一致。特别是，在异相氧化一周后，3-13%的颗粒相碳流失到气相中。我们的结果表明，氧化老化是颗粒有机碳的一个重要汇，更广泛地说，裂解反应在大气有机碳的生命周期中发挥着重要作用。
Atmospheric oxidation reactions are known to affect the chemical composition of organic aerosol (OA) particles over timescales of several days, but the details of such oxidative aging reactions are poorly understood. In this study we examine the rates and products of a key class of aging reaction, the heterogeneous oxidation of particle-phase organic species by the gas-phase hydroxyl radical (OH). We compile and reanalyze a number of previous studies from our laboratories involving the oxidation of single-component organic particles. All kinetic and product data are described on a common basis, enabling a straightforward comparison among different chemical systems and experimental conditions. Oxidation chemistry is described in terms of changes to key ensemble properties of the OA, rather than to its detailed molecular composition, focusing on two quantities in particular, the amount and the oxidation state of the particle-phase carbon. Heterogeneous oxidation increases the oxidation state of particulate carbon, with the rate of increase determined by the detailed chemical mechanism. At the same time, the amount of particle-phase carbon decreases with oxidation, due to fragmentation (C-C scission) reactions that form small, volatile products that escape to the gas phase. In contrast to the oxidation state increase, the rate of carbon loss is nearly uniform among most systems studied. Extrapolation of these results to atmospheric conditions indicates that heterogeneous oxidation can have a substantial effect on the amount and composition of atmospheric OA over timescales of several days, a prediction that is broadly in line with available measurements of OA evolution over such long timescales. In particular, 3-13% of particle-phase carbon is lost to the gas phase after one week of heterogeneous oxidation. Our results indicate that oxidative aging represents an important sink for particulate organic carbon, and more generally that fragmentation reactions play a major role in the lifecycle of atmospheric OA.