Nitrous oxide (N2O) is an atmospheric trace gas that contributes to the greenhouse effect. It is also involved in the catalytic destruction of ozone in the stratosphere and is increasing in concentration by about 0.25% per year. The increase is believed to result from fertilizer use, emissions from internal combustion engines, biomass burning, and industrial processes (Khalil 1995). It is naturally produced by nitrification and denitrification in soils and in the oceans, and is destroyed in the stratosphere via photolysis (90%) and reaction with excited atomic oxygen [O(1D)] (10%). Its atmospheric lifetime is between 100 and 150 years. Although the major sources and sinks of N2O are known, they are poorly quantified and inadequately balanced, both in terms of mass exchange and in their N and O isotopic composition.
Stable isotopes have been used in the past to constrain sources and sinks of other atmospheric trace gases but have yet to be successfully applied to N2O. The isotopic approach to a global N2O budget is hindered by the wide range of observed isotopic values for each of the major natural sources, making it difficult to assign a unique value to each of the source terms. Soil flux samples have been shown to be variable but consistently depleted in both 15N and 18O relative to atmospheric N2O. ...Show more