Microenvironment-Driven Charge Tuning at Microdroplet Interfaces Dictates Criegee Intermediate Reactivity.

Water microdroplets exhibit a wide range of unique physicochemical properties. The charge transfer induced by their high interfacial electric field (∼10 V/m) has been long regarded as the primary mechanism driving their unusual chemical reactivity; however, whether other key factors regulate charge transfer and reaction activity remains an open question. Here, by integrating quantum chemical calculations, advanced enhanced sampling methods, molecular dynamics simulations, and reaction kinetic theory, we reveal that the interfacial microenvironment modulates the charge distribution of electrophilic carbon atoms, leading to remarkable differences in interface-to-gas-phase reaction rate ratios by up to 6 orders of magnitude among Criegee intermediates (CIs) with varying structures. This interfacial catalysis displays remarkable molecular size selectivity: small CIs (e.g., CHOO and CHCHOO) exhibit 4-6 order-of-magnitude enhancements in rate ratios, whereas larger CIs show negligible response. Mechanistic investigations confirm that this selective catalysis originates from the differential regulation of charge distribution characteristics and dynamic fluctuations at the electrophilic carbon center by the interfacial microenvironment. These findings elucidate the role of microdroplet interfacial microenvironments in charge regulation, providing an important complement to the electric field-dominated perspective and offering a theoretical basis for accurate descriptions of particle-phase CIs chemistry in atmosphere.