The destruction of dichloromethane by a nonthermal plasma in atmospheric-pressure gas streams of nitrogen with variable amounts of added oxygen has been investigated. The identities and concentrations of the end products are determined by on-line FTIR spectroscopy, and the plasma chemistry is interpreted using a kinetic modeling scheme. Peak destructions of 20% are found for a deposited energy of 66 J L-1. The maximum dissociation is found for a carrier gas that contains 1-3% O-2, and the dissociation is greater in pure nitrogen than in an air stream. The major end products of the processing are HCN, Cl-2 and HCl in pure nitrogen and CO, COCl2, HCl, and Cl-2 for gas streams containing oxygen. The plasma processing in streams containing oxygen also produces significant yields of nitrogen oxides. The mechanism of dichloromethane destruction in the plasma is predominantly oxidation initiated by atomic chlorine that is produced by collisions of dichloromethane with electronically excited nitrogen atoms and molecules. Because of low cross sections, electron attachment does not play a role in the destruction of dichloromethane. The addition of oxygen to the gas streams initially causes additional destruction from O and OI-I reactions, but further increase in the oxygen concentration causes inhibition of both the atomic chlorine cycle and the formation of NOx and a consequent reduction in dichloromethane destruction.