Vertical profiles of nitrous oxide isotopomer fractionation measured in the stratosphere

We have measured the vertical profiles of several isotopomers of nitrous ox ide, N2O, in the stratosphere by balloon-borne infrared remote sensing betw een 15 and 35 km. In particular we distinguish the individual profiles and relative enrichments of the positional isotopomers (NNO)-N-15-N-14-O-16 and (NNO)-N-14-N-15-O-16 for the first time. We find a distinct and reproducib le relative enrichment of the isotopomers which is in general agreement wit h measured photolysis rates in the laboratory and theoretical predictions. The results confirm photolysis as the dominant stratospheric Loss process f or N2O and argue against suggestions that additional chemical sources of N2 O in the stratosphere are required to explain the observed heavy isotopic e nrichments there.