Strong electric field force at the air/water interface drives fast sulfate production in the atmosphere

How tiny aqueous aerosol droplets significantly accelerate the atmospheric multiphase reaction remains an open question. Here, we show both experimental and theoretical evidence that the strong electric field at the air/water interface of aerosol particles can be an important driving force contributing to the fast oxidation of SO₂-forming sulfate. We mapped out the spatial surface enrichment of sulfate in nitrate microdroplets using 2D laser confocal Raman microscopy and molecular dynamics (MD) simulations. Strong electric fields up to ∼1 × 10⁸ V cm⁻¹ are determined for the aerosol air/water interface, thus highlighting an important role of electrostatic force in atmospherically relevant chemistry. The detailed SO₂ oxidation reaction mechanism triggered by the electric field was further elucidated by density functional theory (DFT) calculations. Overall, this work provides a new perspective, we think, about chemical reactions in the atmosphere and may potentially change the framework of current knowledge concerning the atmospheric chemical process. © 2023 Elsevier Inc.