Kroll Jesse H, Chan Arthur W H, Ng Nga L, Flagan Richard C, Seinfeld John H
Department of Environmental Science and Engineering, California Institute of Technology, Pasadena, California 91125, USA.
Environ Sci Technol. 2007 May 15;41(10):3545-50. doi: 10.1021/es062059x.
Secondary organic aerosol (SOA) constitutes a significant fraction of total atmospheric particulate loading, but there is evidence that SOA yields based on laboratory studies may underestimate atmospheric SOA. Here we present chamber data on SOA growth from the photooxidation of aromatic hydrocarbons, finding that SOA yields are systematically lower when inorganic seed particles are not initially present. This indicates that concentrations of semivolatile oxidation products are influenced by processes beyond gas-particle partitioning, such as chemical reactions and/or loss to chamber walls. Predictions of a kinetic model in which semivolatile compounds may undergo reactions in both the gas and particle phases in addition to partitioning are qualitatively consistent with the observed seed effect, as well as with a number of other recently observed features of SOA formation chemistry. The behavior arises from a kinetic competition between uptake to the particle phase and reactive loss of the semivolatile product. It is shown that when hydrocarbons react in the absence of preexisting organic aerosol, such loss processes may lead to measured SOA yields lower than would occur under atmospheric conditions. These results underscore the need to conduct studies of SOA formation in the presence of atmospherically relevant aerosol loadings.
二次有机气溶胶（SOA）在大气颗粒物总量中占很大比例，但有证据表明，基于实验室研究得出的SOA产率可能低估了大气中的SOA。在此，我们展示了芳香烃光氧化生成SOA增长的实验数据，发现当初始不存在无机种子颗粒时，SOA产率会系统性降低。这表明半挥发性氧化产物的浓度受气粒分配之外的过程影响，如化学反应和/或向反应室壁的损失。一个动力学模型预测，除了分配外，半挥发性化合物可能在气相和颗粒相中都发生反应，这在定性上与观察到的种子效应以及其他一些最近观察到的SOA形成化学特征一致。这种行为源于颗粒相吸收与半挥发性产物反应损失之间的动力学竞争。结果表明，当烃类在不存在预先存在的有机气溶胶的情况下反应时，这种损失过程可能导致测得的SOA产率低于大气条件下的产率。这些结果强调了在存在与大气相关的气溶胶负荷情况下进行SOA形成研究的必要性。
