The multiphase oxidation of SO₂ to sulfate in aerosol particles is a key process in atmospheric chemistry. However, there is a large gap between the observed and simulated sulfate concentrations during severe haze events. To fill in the gaps in understanding SO₂ oxidation chemistry, a combination of experiments and theoretical calculations provided evidence for the direct, spin-forbidden excitation of SO₂ to its triplet states using UVA photons at an air–water interface, followed by reactions with water and O₂ that facilitate the rapid formation of sulfate. The estimated reaction energy for the whole process, ³SO₂ + H₂O + 1/2O₂ → HSO₄^– + H⁺ (298 K, 1 M), was ΔG_r = −107.8 kcal·mol^–1. Moreover, calculations revealed that this was a multistep reaction involving submerged, small energy barriers (∼10 kcal·mol^–1). These results indicate that photochemical oxidation of SO₂ at the air–water interface with solar actinic light may be an important unaccounted source of sulfate aerosols under polluted haze conditions.

中文翻译：

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空气-水界面处 SO2 的自旋禁止激发引发的快速硫酸盐形成

SO ₂在气溶胶颗粒中多相氧化成硫酸盐是大气化学中的一个关键过程。然而，在严重雾霾事件期间，观察到的和模拟的硫酸盐浓度之间存在很大差距。为了填补对 SO ₂氧化化学理解的空白，实验和理论计算的结合提供了证据，证明在空气-水界面使用 UVA 光子将 SO ₂直接、自旋禁止激发到其三重态，然后与促进硫酸盐快速形成的水和O _{2 。}整个过程的估计反应能量，³ SO ₂ + H ₂ O + 1/2O ₂→ HSO ₄ ^– + H ⁺ (298 K, 1 M), 为 Δ G _r = −107.8 kcal·mol ^–1。此外，计算表明，这是一个涉及淹没的小能垒 (∼10 kcal·mol ^–1 ) 的多步反应。这些结果表明，空气-水界面处SO _{2与太阳光化性光的光化学氧化可能是污染雾霾条件下硫酸盐气溶胶的一个重要的未知来源。}