The removal of ozone and other gaseous criteria pollutants from ambient air by a wide variety of catalysts coated on vehicle radiators has been studied utilizing a laboratory reactor and a synthetic feedstream. The experimental conditions simulated driving a vehicle at a low speed through polluted urban air with the radiator temperature varying from 25 to 105 degrees C. The results showed that the ozone removal efficiency was high for all of the catalysts (Pt, Pd, Pd/Ni and Ni) under conditions characteristic of fully warmed-up radiators. The addition of water vapor into the feedstream significantly suppressed the O-3 conversion efficiency at low temperatures for Pt, Pd/Ni and Ni. The Pd-only catalyst demonstrated not only the highest O-3 conversion efficiency among the catalysts tested, but also showed a strong resistance to the inhibition of the O-3 conversion reaction by water vapor at low temperatures. The NO conversion efficiency was significant for all of the catalysts and was suppressed for most of the catalysts by water vapor at low temperatures. The NO2 formation varied with catalyst formulation over the 25-105 degrees C range and was affected by water vapor. The CO (or C3H6 as hydrocarbon) removal, while dependent on catalyst formulation, was a strong function of catalyst temperature, and suppressed by H2O. The Pt catalyst exhibited the highest CO (or C3H6) removal efficiency at elevated temperatures under the dry or wet conditions among the catalysts tested.