Polycyclic aromatic hydrocarbons (PAHs) are widespread and toxic pollutants. Naphthalene is the most abundant PAH found in polluted urban areas. In this Letter, we studied the mechanism for the NO3-initiated atmospheric oxidation reactions of naphthalene, using high-level molecular orbital theory. Geometries of the reactants, intermediates, transition states, and products have been optimized at the BB1K level with the 6-31+G(d,p) basis set. The single-point energy calculations have been carried out at the BB1K/6311+G(3df,2p) level. Several energetically favorable reaction pathways were revealed for the first time. The calculated results were compared with the available experimental observation. (c) 2006 Elsevier B.V. All rights reserved.