Rapid N₂O Formation from N₂ on Water Droplet Surfaces

Nitrogen (N₂) 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 (O₂) at typical tropospheric concentrations can rapidly activate N₂, leading to substantial production of nitrous oxide (N₂O), 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 (O₃), typically consumed by N₂O in the stratosphere, can further accelerate N₂O formation. In contrast, the produced N₂O concentration is below detection limits in the absence of O₂/O₃ or water droplets. A novel reduction-then-oxidation (RTO) mechanism was proposed to account for the rapid formation of N₂O on the water droplet surfaces facilitated by the cooperation of water droplets and O₂/O₃. Further extrapolation indicates that the RTO pathway contributes several Tg N N₂O annually, far exceeding the most known sources of N₂O. These findings have broad implications for tracing atmospheric N₂O sources, enhancing understanding of climate-O₂/O₃ interactions, and paving avenues for developing new methodologies for N₂O synthesis.