The acid displacement reaction of formic acid in sea-salt aerosols to release hydrogen chloride is an enigma in atmospheric chemistry: a weak acid transfers a proton to the conjugate base of a strong acid, reversing solution-phase acid–base chemistry. We show that a surface defect of the crystal lattice Na13Cl12+

We explored the gas-phase ion chemistry of hydrated electron in the reaction with a prototypical organosulphur compounds, i.e. dimethyl disulphide. We showed that the overall reaction is gated by a critical S···H hydrogen bond, which enables a kinetically challenging electron transfer step. The overall exothermicity is not driven