Enhanced Rates of Transition-Metal-Ion-Catalyzed Oxidation of S(IV) in Aqueous Aerosols: Insights into Sulfate Aerosol Formation in the Atmosphere,Environmental Science & Technology

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Enhanced Rates of Transition-Metal-Ion-Catalyzed Oxidation of S(IV) in Aqueous Aerosols: Insights into Sulfate Aerosol Formation in the Atmosphere
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2021-07-19 , DOI: 10.1021/acs.est.1c01932
Kyle J Angle ₁ , Erin E Neal ₁ , Vicki H Grassian ₁

Affiliation

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 (SO₃^2–/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.

中文翻译：

水气溶胶中过渡金属离子催化氧化 S(IV) 的提高速率：对大气中硫酸盐气溶胶形成的洞察

S(IV) 的氧化是决定大气中硫酸盐气溶胶量的二氧化硫排放命运的关键步骤。在此，我们测量了与散装溶液相比，微米级水性气溶胶中加速的 S(IV) 氧化速率。我们研究了在大气相关过渡金属离子和盐存在的情况下，在一系列 pH 值范围内的缓冲和非缓冲系统，并一致发现氧化速率会加快约气溶胶中的 1-2 个数量级。这种增强作用大于气溶胶中物质的富集程度，这表明表面效应和潜在的气溶胶 pH 梯度在水性气溶胶中的 S(IV) 氧化过程中起着重要作用。此外，₃^2– /HSO ₃^– )，使我们能够证明在凝聚相中发生加速，这表明硫酸盐形成的增强不仅仅归因于气溶胶分配或界面 SO ₂氧化。我们的发现是在理解大气中观察到的大于预期的硫酸盐浓度方面向前迈出的重要一步，并表明与本体溶液相比，微米级水滴中的无机氧化过程可以加速。

更新日期：2021-08-03

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