Aromatic hydrocarbons (AHs) are widespread and toxic pollutants. Benzene is the most abundant AHs found in polluted urban areas. In this Letter, we studied the mechanism for the oxidation degradation of benzene by NO3 radicals in the nighttime atmosphere. The profile of the potential energy surface was constructed, and all of the possible channels were discussed. Geometries have been optimized at the BB I K level with the 6-31 + G(d,p) basis set. The single-point energy calculations have been carried out at the BB1K/6-311 + G(3df, 2p) level. The possible secondary reactions were also studied. The formation mechanism of secondary pollutants from the radical-initiated reaction was also revealed. (c) 2006 Elsevier B.V. All rights reserved.