Sulfate Promotes Amine Salt Ozonation in Atmospheric Aerosols

Low molecular weight amines promote sulfate (SO₄^2- and HSO₄^-) formation through acid-base reactions, contributing to fine particulate matter (PM). Heterogeneous ozonation converts nontoxic amine salts into highly toxic products, yet the ozonation activation mechanism is unclear. This work reveals a sulfate-dominant ozonation mechanism of amine salts in fine PM by combining advanced mass spectrometry and ab initio calculation methods. With the synergy of ^•OH-initiated oxidation, SO₄^2- activates amine ions through deprotonation, producing imine molecules as ozonation intermediates. Subsequently, HSO₄^- accelerates the formation of the intermediate aminomethanol and ozonation products. Moreover, this novel ozonation mechanism of amine salt is verified to be efficient for sulfate fine PM and is not feasible for chloride or nitrate fine PM. In this study, the key role of sulfate in the ozonation of inert organic compounds is highlighted, which needs to be considered in fine PM chemistry.