Absence of isotope exchange in the reaction of N2O + O(1D) and the global Δ17O budget of nitrous oxide

Yung et al. (2004) suggested that N2O exchanges isotopes with O(1D), analogous to CO2, which would represent an additional contribution to the 17O isotope anomaly of atmospheric N2O. Here we demonstrate by isotope measurements of N2O remaining after partial conversion with O(1D) that this isotope exchange most likely proceeds at <1% of the total N2O + O(1D) reaction rate. It can therefore be neglected as a source of the 17O anomaly of atmospheric N2O, corroborating arguments based on previous indirect experimental evidence of the absence of such isotope exchange (Röckmann and Kaiser, 2005). In addition, we present a balanced budget of the 17O anomaly of atmospheric N2O, based on N2O sources at Earth's surface and in the atmosphere: the reactions of N2 + O(1D) + M, NH2 + NO2, and N + NO2, industrial processes, biomass burning, and the “numerical” source from microbial nitrogen conversion reactions (Kaiser et al., 2004b).