Characterizing N₂O₅ Reactivity at Aerosol Interfaces Using Water Cluster Model Systems

The heterogenous reactions of dinitrogen pentoxide (N₂O₅) occurring at the air-water interface of sea spray aerosol (SSA) play a key role in the regulation of gas-phase oxidants and greenhouse gases in the atmosphere. Despite the importance of such reactions, existing atmospheric models consistently fail to reproduce the highly variable rates and product yields observed in ambient SSA, highlighting the disconnect between current predictive parameterizations and the processes they describe. Here, we characterize interfacial reactivity at the molecular level by implementing a custom-designed dual ion trap mass spectrometer to investigate the reactions between size-selected I^-(D₂O)_n=0-10 cluster model systems and N₂O₅ at well-defined temperatures and collision energies. In doing so, we reveal the chemical speciation of N₂O₅ as a function of cluster size and clarify the role of humidity in the chemical ionization detection method currently used for its field observation.