Measurement of isotopic abundances in collected stratospheric ozone samples

Enrichment of heavy O 3 isotopes has been measured in collected stratospheric samples. A balloon‐borne cryogenic sampler was used to gather six O 3 samples between 26 and 35 km in three flights. Subsequent laboratory mass spectrometer analysis of rare O 3 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, 50 O 3 was enriched by 12–16% and 49 O 3 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 O 3 at mass 50 are less than the large 40% value observed in some stratospheric measurements but similar to 49 O 3 and 50 O 3 fractionations produced in laboratory‐generated ozone.