Enhanced Rates of Transition-Metal-Ion-Catalyzed Oxidation of S(IV) in Aqueous Aerosols: Insights into Sulfate Aerosol Formation in the Atmosphere
Enhanced Rates of Transition-Metal-Ion-Catalyzed Oxidation of S(IV) in Aqueous Aerosols: Insights into Sulfate Aerosol Formation in the Atmosphere
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DOI：
10.1021/acs.est.1c01932
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发表时间：
2021-07-19
影响因子：
11.4
通讯作者：
Grassian, Vicki H.
中科院分区：
文献类型：
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作者：
Angle, Kyle J.;Neal, Erin E.;Grassian, Vicki H.
S（IV）的氧化是二氧化硫排放的关键步骤，它决定了大气中硫酸盐气溶胶的数量。在这里，我们测量了在微米大小的水性气溶胶中与散装溶液相比加速的S（IV）氧化速率。我们研究了在与大气相关的过渡金属离子和盐存在的pH值范围内的缓冲和非缓冲系统，并一致发现在气溶胶中氧化速率加快了约1-2个数量级。这种增强比气溶胶中物质的富集更能解释，表明表面效应和潜在的气溶胶pH梯度在含水气溶胶中的S（IV）氧化过程中起重要作用。此外，我们的实验是用溶解的S（IV）离子（SO32-/HSO3-）进行的，这使我们能够证明加速发生在凝聚相中，这表明硫酸盐的形成并不完全是由于气体-气溶胶分配或界面SO2氧化。我们的发现在理解大气中观察到的大于预期的硫酸盐浓度方面迈出了重要的一步，并表明与散装溶液相比，微米级水溶液中的无机氧化过程可以加速。
The oxidation of S(IV) is a critical step in the fate of sulfur dioxide emissions that determines the amount of sulfate aerosol in the atmosphere. Herein, we measured accelerated S(IV) oxidation rates in micron-sized aqueous aerosols compared to bulk solutions. We have investigated both buffered and unbuffered systems across a range of pH values in the presence of atmospherically relevant transition-metal ions and salts and consistently found the oxidation rate to be accelerated by ca. 1-2 orders of magnitude in the aerosol. This enhancement is greater than can be explained by the enrichment of species in the aerosol compared to the bulk and indicates that surface effects and potentially aerosol pH gradients play important roles in the S(IV) oxidation process in the aqueous aerosol. In addition, our experiments were performed with dissolved S(IV) ions (SO32-/HSO3-), allowing us to demonstrate that acceleration occurs in the condensed phase showing that enhanced sulfate formation is not exclusively due to gas-aerosol partitioning or interfacial SO2 oxidation. Our findings are an important step forward in understanding larger than expected sulfate concentrations observed in the atmosphere and show that inorganic oxidation processes can be accelerated in micron-sized aqueous droplets compared to the bulk solution.