Carbon dioxide is one of the main gaseous products in oxidation of carbonaceous materials via both homogeneous and heterogeneous reactions. However, the mechanisms of heterogeneous CO2 evolution during oxidation of aromatic carbon-based materials are not known in detail. Using density functional theory, a new oxidation mechanism of aromatic hydrocarbons with atomic oxygen was suggested to consist of four main steps, namely, (1) adsorption of oxygen atom, (2) insertion of O atom into the ring, (3) rearrangement to form a five-membered ring and four-membered ring lactone group, and (4) desorption of CO2. Using naphthoxy radical as a model system, the proposed reaction pathway can explain how some of the experimentally observed CO2 is formed.