Department of Land, Air, and Water Resources, University of California, Davis, California 95616, United States.
Department of Environmental Toxicology, University of California, Davis, California 95616, United States.
Environ Sci Technol. 2021 May 4;55(9):5772-5781. doi: 10.1021/acs.est.1c00575. Epub 2021 Apr 14.
Biomass burning emits large amounts of phenols, which can partition into cloud/fog drops and aerosol liquid water (ALW) and react to form aqueous secondary organic aerosol (aqSOA). Triplet excited states of organic compounds (C*) are likely oxidants, but there are no rate constants with highly substituted phenols that have high Henry's law constants () and are likely important in ALW. To address this gap, we investigated the kinetics of six highly substituted phenols with the triplet excited state of 3,4-dimethoxybenzaldehyde. Second-order rate constants at pH 2 are all fast, (2.6-4.6) × 10 M s, while values at pH 5 are 2-5 times smaller. Rate constants are reasonably described by a quantitative structure-activity relationship with phenol oxidation potentials, allowing rate constants of other phenols to be predicted. Triplet-phenol kinetics are unaffected by ammonium sulfate, sodium chloride, galactose (a biomass-burning sugar), or Fe(III). In contrast, ammonium nitrate increases the rate of phenol loss by making hydroxyl radicals, while Cu(II) inhibits phenol decay. Mass yields of aqueous SOA from triplet reactions are large and range from 59 to 99%. Calculations using our data along with previous oxidant measurements indicate that phenols with high can be an important source of aqSOA in ALW, with C* typically the dominant oxidant.
生物质燃烧会排放大量的酚类物质，这些酚类物质可以分配到云/雾滴和气溶胶液态水中（ALW），并发生反应形成水相二次有机气溶胶（aqSOA）。有机化合物的三重激发态（C*）很可能是氧化剂，但对于具有高亨利定律常数（）的高取代酚类物质，目前还没有与之相关的速率常数，而这些物质在 ALW 中很可能很重要。为了解决这一差距，我们研究了六种具有 3,4-二甲氧基苯甲醛三重激发态的高取代酚类物质的动力学。在 pH 值为 2 时，它们的二级速率常数都很快，（2.6-4.6）×10^M s^-1，而在 pH 值为 5 时，这些速率常数要小 2-5 倍。速率常数可以通过与酚类氧化电位的定量结构活性关系得到合理描述，从而可以预测其他酚类物质的速率常数。三重态-酚类物质动力学不受硫酸铵、氯化钠、半乳糖（一种生物质燃烧糖）或 Fe（III）的影响。相比之下，硝酸铵通过产生羟基自由基来增加酚类物质的损失速率，而 Cu（II）则抑制酚类物质的降解。三重态反应生成的水相 SOA 的质量产率很大，范围从 59%到 99%。利用我们的数据和以前的氧化剂测量结果进行计算表明，具有高的酚类物质可以成为 ALW 中 aqSOA 的重要来源，其中 C*通常是主要的氧化剂。
