Observation of a mass independent oxygen isotopic composition in terrestrial stratospheric CO 2 , the link to ozone chemistry, and the possible occurrence in the Martian atmosphere

Multi‐isotope (δ 17 O and δ 18 O) measurements of stratospheric CO 2 and 14 CO are reported. Samples were acquired from altitudes in excess of 11.5 km from Christchurch, New Zealand to the South Pole. A mass independent isotopic variation is observed in CO 2 , the magnitude of which correlates well with 14 CO concentration, indicating a stratospheric source of the effect. The component arises from isotopic exchange between the product of O 3 photolysis, O(¹D) and CO 2 thus providing a unique measure of ozone photolysis and turnover. A similar process may occur in the Martian atmosphere, as suggested by water isotopic measurements from SNC meteorites.