Interfacial Nitrate Photolysis Drives Rapid Oxidation of Organic Carbon.

Sunlight-driven photochemical reactions are a major force driving atmospheric and aquatic cycles of organic carbon (OC), and affect Earth's climate. However, current OC photo-oxidation flux assessment relying on bulk-phase kinetics systematically underestimate reaction rates observed in nature. It remains uncertain whether the environmental interfaces are the driving variables regulating OC photo-processing rates. Here we demonstrate that photolysis of nitrate (NO3-) at air-water interfaces establishes a highly efficient and previously unrecognized pathway for rapid OC transformation. Using both volatile and dissolved organic carbon (VOCs and DOCs) as model substrates, we demonstrate that NO3- photolysis in microdroplets drives a unified enhancement in oxidative reactivity, accelerating VOCs oxidation by 6.9-17.0-fold and increasing DOCs mineralization efficiency by ∼5.1-fold. Confocal Raman and fluorescence imaging further show the co-enrichment of NO3- and OC in interfacial layer, creating a confined and highly reactive region for rapid OC photo-oxidation. This observation challenges the long-standing practice of using bulk reaction kinetics for assessing OC processing rates, and instead lends evidence for air-water interfaces as hotspot for significantly accelerated OC transformation in nature, understanding of carbon cycle rates in atmospheric and aquatic systems.