Interfacial Nitrate Photolysis Drives Rapid Oxidation of Organic Carbon

Abstract 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.