MASS-INDEPENDENT OXYGEN-ISOTOPE FRACTIONATION IN ATMOSPHERIC CO AS A RESULT OF THE REACTION CO+OH

Atmospheric carbon monoxide (CO) exhibits mass-independent fractionati on in the oxygen isotopes. An O-17 excess up to 7.5 per mil was observ ed in summer at high northern latitudes. The major source of this puzz ling fractionation in this important trace gas is its dominant atmosph eric removal reaction, CO + OH --> CO2 + H, in which the surviving CO gains excess O-17. The occurrence of mass-independent fractionation in the reaction of CO with OH raises fundamental questions about kinetic processes. At the same time the effect is a useful marker for the deg ree to which CO in the atmosphere has been reacting with OH.