NO2 adsorption on activated carbons at ambient temperature was studied. The adsorbed species after various adsorption times were examined by analyzing the evolution of NO, NO2, CO, CO2, and O-2 during thermal desorption. Emission of NO but not NO2 was observed during the early stage of NO2 adsorption. From the nitrogen and oxygen balance data, we conclude that NO2 adsorption involves the reduction of NO2 to NO driven by oxidation of the carbon surface. The formed NO is either adsorbed on the carbon surface or released as exhaust gas depending on the surface conditions. The adsorbed NO species are released along with O-2 and a small amount of CO2 and CO at temperatures below 150 degrees C during heating. NO2 becomes stable when the carbon surface has been extensively oxidized.