Photodegradation of halobenzenes in water ice

Results from the photolysis of o, p-dichlorobenzene, bromobenzene, and p-di bromobenzene in water ice are reported. All phototransformations appeared t o be based on dehalogenation, coupling, and rearrangement reactions in ice cavities. No photosolvolysis products, i.e. products from intermolecular re actions between organic and water molecules, were found. Many of the produc ts were very toxic substances of a high environmental risk, such as PCBs. T he results support our model, in which secondary, very toxic, pollutants ca n be formed in ice, snow, an atmospheric ice particles from primary polluta nts through the action of solar irradiation. The photoproducts may be relea sed to the environment by ice melting and evaporation.