Rapid N₂O Formation from N₂ on Water Droplet Surfaces

Abstract Nitrogen (N 2 ) has long been considered as stable atmospheric reservoir for N element and has a persistence time of hundreds of years. This study reveals that oxygen (O 2 ) at typical tropospheric concentrations can rapidly activate N 2 , leading to substantial production of nitrous oxide (N 2 O), the third most impactful greenhouse gas, at rates approaching 2.83±0.41 ppmv hour −1 catalyzed by ubiquitous water droplets in experimental systems. Notably, ozone (O 3 ), typically consumed by N 2 O in the stratosphere, can further accelerate N 2 O formation. In contrast, the produced N 2 O concentration is below detection limits in the absence of O 2 /O 3 or water droplets. A novel reduction‐then‐oxidation (RTO) mechanism was proposed to account for the rapid formation of N 2 O on the water droplet surfaces facilitated by the cooperation of water droplets and O 2 /O 3 . Further extrapolation indicates that the RTO pathway contributes several Tg N N 2 O annually, far exceeding the most known sources of N 2 O. These findings have broad implications for tracing atmospheric N 2 O sources, enhancing understanding of climate‐O 2 /O 3 interactions, and paving avenues for developing new methodologies for N 2 O synthesis.