In this Letter, we present the investigation of the potential energy surface for the ONO-NO2 molecule and the asymmetric dimerization of NO2 by using the DFT/B3LYP methodology. The torsion energy of the ONO-NO2 isomer is 1.7 kcal mol(-1). The asymmetric dimerization of NO2 is barrierless with an energy well of 19.8 kcal mol(-1). By using the polarizable continuum model, the NO, asymmetric dimerization in aqueous phase may be slightly spontaneous. From this study, we suggest that this reaction is likely to occur in aqueous phase of polluted environments. (c) 2007 Elsevier B.V. All rights reserved.