Rapid Formation of Nitric Sulfuric Ester at the Gas–Liquid Interface and Its Potential Contribution to Aerosol Growth

Owing to the large surface-to-volume ratio and unsaturated hydrogen-bonding network, interfacial water molecules can markedly accelerate many reactions in the gas phase. Although the gas-phase reaction between sulfur trioxide (SO 3 ) and nitric acid (HNO 3 ) has been shown to compete with the SO 3 + 2H 2 O and OH + HNO 3 reactions at altitudes of 25–35 km, its interfacial mechanisms remain elusive. Herein, classical molecular dynamics (MD) simulations and Born–Oppenheimer molecular dynamics (BOMD) simulations were employed to elucidate the adsorption behavior and interfacial reactivity of SO 3 and HNO 3 at the gas–liquid interface. MD simulations reveal strong interfacial preference for both species, characterized by their lowest free energies and high aggregation probabilities. BOMD results show that the interfacial reaction between SO 3 and HNO 3 rapidly produces O 2 NOSO 3 – on the picosecond time scale, a pathway significantly more favorable than the gas-phase reaction and competitive with SO 3 hydrolysis. Moreover, the resulting O 2 NOSO 3 – exhibits stronger binding to SA–A clusters than other common species, thereby facilitating aerosol particle growth. This work provides a new insight into SO 3 consumption in HNO 3 -polluted regions and the potential roles of sulfate compounds in aerosol growth.