Reactive uptake of N2O5 by atmospheric aerosol is dominated by interfacial processes

On the surfaceThe uptake and hydrolysis of N2O5 from the atmosphere by aqueous aerosols was long thought to occur by solvation and subsequent hydrolysis in the bulk of the aerosol. However, this mechanistic hypothesis was unverifiable because of the fast reaction kinetics. Galib et al. used molecular simulations to show instead that the mechanism is the inverse: Interfacial hydrolysis is followed by solvation into the interior. Their reactive uptake model is consistent with some existing experimental observations.Science, this issue p. 921Nitrogen oxides are removed from the troposphere through the reactive uptake of N2O5 into aqueous aerosol. This process is thought to occur within the bulk of an aerosol, through solvation and subsequent hydrolysis. However, this perspective is difficult to reconcile with field measurements and cannot be verified directly because of the fast reaction kinetics of N2O5. Here, we use molecular simulations, including reactive potentials and importance sampling, to study the uptake of N2O5 into an aqueous aerosol. Rather than being mediated by the bulk, uptake is dominated by interfacial processes due to facile hydrolysis at the liquid-vapor interface and competitive reevaporation. With this molecular information, we propose an alternative interfacial reactive uptake model consistent with existing experimental observations.