The reactions of CF3Cl, CF2Cl2, CFCl3, and CCl4 with gamma-alumina powders have been studied using temperature-programmed reaction (TPR) and X-ray photoelectron (XPS) spectroscopies. In the TPR experiments, powder samples that had been dehydroxylated by healing to 1000 K in vacuum were dosed at 100 K with halomethanes and then gradually heated. Desorbing species were monitored as a function of substrate temperature using a line-of-sight quadrupole mass spectrometer. Hydrogen chloride and halomethyl fragments, which are indicative of halomethane dissociative chemisorption, were observed to desorb at temperatures below 150 K. Carbon dioxide began to desorb between 240 and 320 K; the onset temperature of CO2 desorption correlated inversely with the degree of chlorination of the compound. The CO2 most likely arises from COn (carbonate and/or formate) species which are formed via the low-temperature dissociative chemisorption of the halomethanes. Repeated heating and dosing of the alumina sample resulted in a drop in CO2 production, implying that surface active sites become depleted. In situ XPS analysis of heat-treated powders that had been dosed at 150 K with chlorofluoromethanes revealed the presence of both organic and inorganic forms of fluorine. Powders dosed at 200 K had much lower organic halogen coverages. Halogen uptake probabilities, which are estimated to be similar to 10(-5) from the data, increased as the degree of chlorination of the halomethane increased. These results indicate that chlorofluoromethane compounds will probably decompose on alumina solid-propellant rocket motor exhaust particles in the stratosphere, forming adsorbed AI-X (X = F, CI) and COn species and releasing gas phase HCl and CFxCly fragments. However, the impact of these processes on global stratospheric halomethane and ozone concentrations is likely to be minimal.