N₂O is not only a potent greenhouse gas — it is currently the dominant ozone-depleting substance (ODS) emitted by human activities. This dual role makes it uniquely important in atmospheric chemistry, connecting two of the most critical environmental challenges of our era.
The NOₓ Mechanism
When N₂O reacts with excited oxygen atoms O(¹D) in the stratosphere, it produces nitric oxide (NO). NO catalytically destroys ozone through a well-established chain reaction: NO + O₃ → NO₂ + O₂, followed by NO₂ + O → NO + O₂. The net result is ozone destruction while NO is regenerated to continue the cycle.
N₂O ODP (ozone depletion potential): 0.017
N₂O current ODS contribution: ~largest single source
N₂O-derived NOₓ share of ozone loss: ~33%
Montreal Protocol coverage: excluded
The Montreal Protocol Gap
The Montreal Protocol successfully phased out chlorofluorocarbons (CFCs) and other halogenated ODS, but N₂O was never included — primarily because its agricultural origins made it politically difficult to regulate. Ravishankara et al. (2009, Science) showed that N₂O is now the single largest ozone-depleting emission, a finding that spurred renewed policy discussions about whether N₂O should be addressed under the Protocol’s framework.