NO 2 decomposition on Pt(110) was studied by XPS and TDS at various temperatures. At room temperature, NO 2 decomposes to adsorbed NO and oxygen adatoms on Pt(110). Strong repulsive interactions exist between the adsorbed NO and the oxygen adatoms. Above 450 K, NO a d s desorbs completely from the Pt(110) surface and only adsorbed oxygen is left on the surface. O 2 thermal desorption spectra results reveal that, comparing with oxygen adsorption on Pt(110), NO 2 exposure above 350 K gives rise to an additional oxygen adsorption state on Pt(110) that desorbs at a lower temperature. The new oxygen adsorption state has an O1s binding energy of 529.2 eV. The formation of the new oxygen adsorption state may be associated with the local phase transition of the Pt(110) surface from (1x2) structure to (1x1) structure induced by the NO a d s that is formed from NO 2 decomposition.