Temperature-programmed reaction (TPR) and desorption (TPD) were performed to determine the reaction and adsorption characteristics of NOx, CO, O-2, CO2, and their mixtures on the sensor elements of a WO3/yttria-stabilized-zirconia (YSZ)/Pt potentiometric sensor. The results are discussed, focusing on how sensor performance is influenced by catalytic and adsorptive behavior of the electrode materials. The NO2 sensor response is most likely given by a dissymmetry of the NO2 decomposition activity between the WO3 and Pt electrode. No significant adsorption of NO2 and its related molecules is observed during the TPD of NO2 and NO2-containing gas mixtures. Enhanced NO response by coexisting CO agrees with the increased NO adsorption by the addition of CO, indicating that the NO response is related to gas adsorption behavior. (C) 2006 The Electrochemical Society.