We used ab initio calculations to explore a new path for ion-induced SO₂ oxidation by ozone in the gas phase. We find that, initiated by the superoxide ion, SO₂ can readily oxidize to SO⁻₃. The reaction is facilitated by the presence of water, being ~ 4 orders of magnitude faster than the reaction in the absence of water. Depending on the altitude and temperature, it is estimated that this reaction may contribute to 0.1–2.0 % of the total atmospheric sulfate.