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

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Abstract
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 15N14NO, 15ε1 = 10.9±1.7‰ and 14N15NO, 15ε2 = 35.7±0.5‰ during ultraviolet photolysis at 193 nm, along with the 18O fractionation constant, 18ε = 17.3±0.5‰. Consistent results were obtained over a wide range of experimental conditions. The observed position‐dependent 15N 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.