Isotopic composition of stratospheric ozone

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Abstract
Using recently measured rates for isotopic variants of the ozone formation reaction O + O2 + M, we derive expressions for the enrichment of symmetric and asymmetric 50O3 and 49O3 in stratospheric ozone and calculate total enrichments of 123‰ and 107‰ for 50O3 and 49O3, respectively. We compare the calculations with measurements made with the Smithsonian Astrophysical Observatory far‐infrared spectrometer during seven balloon flights which took place between 1989 and 1997. We find that the calculations are in reasonable agreement with the average observed enrichments of 102±43‰ and 73±60‰ for 50O3 and 49O3, respectively, where the errors indicate the estimated accuracy; we also find that our measurements are in agreement with other recent stratospheric and tropospheric measurements. Using our measurements of the enrichment of the asymmetric and symmetric forms of 50O3 and 49O3, we estimate branching ratios of 0.43±0.03 and 0.46±0.06 for production of the symmetric isotopomer by the reaction of 16O with 34O2 and 33O2, respectively.