A number of experimental studies have been conducted to determine the atmospheric oxidation of tetrachloroethylene, many indicating phosgene as the major product. Although various mechanisms have been suggested, the mechanism of phosgene production is unclear. Additionally, confusion has arisen over the role chlorine atoms may play in the oxidation of tetrachloroethylene and the products produced. To clarify these points, this study presents a comprehensive computational study of both the hydroxyl radical and the chlorine atom initiated atmospheric oxidation mechanism of tetrachloroethylene. The energetics for the oxidation of tetrachloroethylene (C(2)Cl(4)) are computed using ab initio methods. Potential energy surfaces of the reaction pathways are determined from the computations. This study clarifies the involvement of the Cl-initiated reaction pathways in the oxidation of tetrachloroethylene. Results from this work suggest that the final products are primarily from the Cl-initiated oxidation and include: trichloroacetyl chloride [ClC(O)CCl(3)], phosgene [C(O)Cl(2)], and regeneration of the initiating chlorine atom.