Tightening standards for gas-phase environmental pollution necessitate further improvements on the potentiometric NOx sensor. A key component in these improvements involves an analysis of the surface species formed by NOx exposure. Possible NOx adsorption mechanisms on p-type semiconducting La2CuO4 were explored by infrared and X-ray photoelectron spectroscopy. Diffuse reflectance infrared spectroscopy was used to identify charged and uncharged complex formation on the surface of La2CuO4 powder following NO and NO2 adsorption in the presence of oxygen. Subtraction spectra calculated by comparison of adsorbed and unadsorbed KBr/La2CuO4 samples revealed the presence of nitrate and nitrite species as the major product for both adsorptions. X-ray photoelectron spectroscopy examined the difference in bonding between the NO and NO2 adsorption by examination of the O 1s electron orbital. NO was observed to induce oxygen vacancies and reduce the charge carriers in the material by electron injection. NO2 adsorption resulted in the creation of electron holes, which increased charge carrier concentration. (C) 2008 The Electrochemical Society.