Nitrous oxide is currently the dominant ozone-depleting substance (ODS) emitted by human activities, having surpassed the chlorofluorocarbons (CFCs) regulated by the Montreal Protocol. Unlike CFCs, N₂O emissions are not controlled by the Protocol, making it the subject of intense scientific and policy discussion.
Stratospheric Chemistry
In the stratosphere, N₂O reacts with excited atomic oxygen (O*) to produce nitric oxide (NO), which then participates in catalytic ozone destruction cycles. The relevant reactions include:
N₂O + O* → 2NO NO + O₃ → NO₂ + O₂ NO₂ + O → NO + O₂
Implications
Although N₂O’s ozone depletion potential per molecule is much lower than CFCs, its large emission volume makes it a significant contributor. Scientists estimate N₂O causes approximately 5–6% of current stratospheric ozone destruction, and this fraction will grow as CFC levels decline.