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.