The differential enthalpies of adsorption of air pollutants such as SO2, NO2, NO on alumina-supported tin and gallium oxides were measured by calorimetry coupled with isothermal volumetry. Whatever the amount of tin or gallium on alumina, the enthalpies of adsorption of SO2 at low coverage were of the same order of magnitude or up to 50 kJ/mol lower than those of the support. The amount of SO2 adsorbed decreased with increasing SnO2 loading and increased with increasing Ga2O3 loading on the alumina. The differential enthalpies of adsorption of NO2 are close to those on the support whatever the amount of tin or gallium (around 120-130 kJ/mol). NO is only reversibly adsorbed on the samples. The calorimetric data of ammonia adsorption are given for comparison.