Isotopic exchange between carbon dioxide and ozone via O(^1D) in the stratosphere

We propose a novel mechanism for isotopic exchange between CO_2 and O_3 via O(^1D) + CO_2 → CO_3^* followed by CO_3^* → CO_2 + O(^3P). A one-dimensional model calculation shows that this mechanism can account for the enrichment in ^(18)O in the stratospheric CO_2 observed by Gamo et al. [1989], using the heavy O_3 profile observed by Mauersberger [1981]. The implications of this mechanism for other stratospheric species and as a source of isotopically heavy CO_2 in the troposphere are briefly discussed