Interfacial Electric Fields Transform Brown Carbon Formation: Accelerate Radical Coupling toward Strong Light-Absorbing Products

)─a level that surpasses many previously reported pathways. The aging rate can be increased by up to 2 orders of magnitude compared to bulk solutions due to selective radical-radical coupling polymerization. This is driven by promoted intermolecular energy transfer between direction-oriented excited methoxyphenol molecules and reduced energy barriers via stabilized dimer intermediates in the presence of a strong interfacial electric field, as evidenced by high-resolution spectroscopy and quantum calculations. Our study underscores the catalytic role of electric fields in the browning process, reshaping our understanding of atmospheric photochemical aging and highlighting an overlooked driver of BrC formation with far-reaching implications for aerosol reactivity and atmospheric processes.