Measurement of the isotopic fractionation of 15N14N16O, 14N15N16O and 14N14N18O in the UV photolysis of nitrous oxide

The isotopic analysis of atmospheric nitrous oxide (N2O) has become a valuable tool in the investigation of its sources, sinks, and its atmospheric cycle. In particular the considerable isotopic enrichment accompanying stratospheric photolysis of N2O, its dominant atmospheric sink process, Provides a key isotope signal in the construction of a global N2O isotope budget, Here we present the first measurements of the individual fractionation constants for (NNO)-N-15-N-14, (15)epsilon(1) = 10.9+/-1.7 parts per thousand and (NNO)-N-14-N-15, (15)epsilon(2) = 35.7+/-0.5 parts per thousand during ultraviolet photolysis at 193 nm, along with the O-18 fractionation constant, (18)epsilon = 17.3+/-0.5 parts per thousand. Consistent results were obtained over a wide range of experimental conditions. The observed position-dependent N-15 fractionation confirms theoretical predictions and provides a unique signature of N2O that has been processed in the stratosphere, adding a new dimension to an isotope-based description of the atmospheric N2O budget.