The oxidation of nitrogen monoxide has implications for the complex atmospheric chemistry of Antarctica, as well as for planetary atmospheres. In this study we unveil that O-2 adsorbed on a cold surface reacts with a very high efficiency with NO coming from the gas phase to form NO2. Via two molecular beams, O-2 and NO molecules are aimed at a cold (10 K) sample held in a UHV chamber. NO2 is formed independently of the surface composition and morphology. We show that the NO + O-2 reaction occurs mainly through the direct Eley Rideal mechanism to form nitrogen oxides (NO2, N2O3, N2O4). (C) 2013 Elsevier B.V. All rights reserved.