Measurement of isotopic abundances in collected stratospheric ozone samples

Enrichment of heavy O₃ isotopes has been measured in collected stratospheric samples. A balloon‐borne cryogenic sampler was used to gather six O₃ samples between 26 and 35 km in three flights. Subsequent laboratory mass spectrometer analysis of rare O₃ isotopes at both mass 49 and 50 has resulted in more precise measurements than have previously been reported with in situ and ground‐based techniques. In one flight, ⁵⁰O₃ was enriched by 12–16% and ⁴⁹O₃ by 9–11%, both increasing with altitude. In the remaining two flights, the isotope enrichment was nearly mass‐independent at 8–9%. The enrichments in O₃ at mass 50 are less than the large 40% value observed in some stratospheric measurements but similar to ⁴⁹O₃ and ⁵⁰O₃ fractionations produced in laboratory‐generated ozone.