Redox Oscillation-Driven\nProduction of Reactive Oxygen\nSpecies from Black Carbon

Wildfire and stubble burning release substantial amounts\nof black\ncarbon (BC) into natural environments that experience frequent redox\noscillations, such as wetlands and farmlands. Here, we report that\nredox oscillations can effectively drive ROS production from BC. Following\nsequential microbial reduction and air exposure, 6.5 ± 0.2 μM/g<sub>C</sub> hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and 285.3\n± 9.5 nM/g<sub>C</sub> hydroxyl radical (•OH) were produced\nfrom BC. Moreover, BC derived from various biomass sources, temperatures,\nand particle sizes exhibits 111.5-fold variations in ROS production.\nElectrochemical analyses revealed that both the electron transfer\ncapacity and the ROS production selectivity are critical determinants\nof ROS generation under redox oscillations. The variation in electron\ntransfer capacity (0.3–5.7 mmol e<sup>–</sup>/g<sub>C</sub>) is primarily governed by the abundance of electron-storing\nmoieties such as quinones, while the ROS generation selectivity (26.2–72.0%)\nis influenced by the presence of competitive sites for oxygen reduction\nreactions, such as carbon defects. These findings provide insights\ninto ROS production from BC under fluctuating redox conditions, with\npotential implications for elemental cycles and pollutant dynamics\nin regions prone to wildfire and stubble burning events and substantial\nBC deposition (e.g., wetlands and rice paddies).