A study of the adsorption of NO2 on a nanocrystalline tin(IV) oxide powder was carried out in situ by Raman spectroscopy. Heat treatment up to 300 °C of the sample in NO2 revealed the complexity of the surface reactions. Thus, numerous NOx adsorbed species were evidenced such as weakly adsorbed nitrates, NO2 dimers, nitrites, bridging and various bidentate nitrates. The stability of these last species has been related to the NO bond strength. It has been proposed that the nitrite species are responsible for the SnO2 response in the presence of NO2 traces. Copyright © 2006 John Wiley & Sons, Ltd.