We present data that suggest the possibility of a previously unsuspected heterogeneous process involving the decomposition of halocarbon source gases on alumina solid-propellant rocket motor exhaust particles deposited in the stratosphere. These results, obtained under ultrahigh vacuum conditions, provide evidence that halomethane compounds undergo dissociative chemisorption on &agr;-alumina surfaces at stratospheric temperatures, leading to the release of more reactive halogen containing species. Simple calculations indicate that halocarbon concentrations will be severely depleted in the immediate wake of the rocket plume; any serious global impact at current projected launch rates requires the existence of one or more processes that regenerate active sites on the surface subsequent to the dissociative chemisorption of halocarbons.