Hydrogen peroxide serves as pivotal fountainhead for aerosol aqueous sulfate formation from a global perspective.

Abstract

Traditional atmospheric chemistry posits that sulfur dioxide (SO₂) can be oxidized to sulfate (SO₄^2-) through aqueous-phase reactions in clouds and gas-phase oxidation. Despite adequate knowledge of traditional mechanisms, several studies have highlighted the potential for SO₂ oxidation within aerosol water. Given the widespread presence of tropospheric aerosols, SO₄^2- production through aqueous-phase oxidation in aerosol water could have a pervasive global impact. Here, we quantify the potential contributions of aerosol aqueous pathways to global sulfate formation based on the GEOS-Chem simulations and subsequent theoretical calculations. Hydrogen peroxide (H₂O₂) oxidation significantly influences continental regions both horizontally and vertically. Over the past two decades, shifts in the formation pathways within typical cities reveal an intriguing trend: despite reductions in SO₂ emissions, the increased atmospheric oxidation capacities, like rising H₂O₂ levels, prevent a steady decline in SO₄^2- concentrations. Abating oxidants would facilitate the benefit of SO₂ reduction and the positive feedback in sulfate mitigation.