Ultraviolet photodegradation can destroy a wide range of organic compounds and has gained considerable interest for use in reducing environmental pollution. In the present study, ozone-assisted UV photodegradation was developed for the decomposition of gaseous ethylbenzene (EB) and chlorobenzene (CB). The effects of various experimental parameters were investigated, namely initial concentration, initial ozone addition, relative humidity, and reaction time. The results showed that an ozone/EB ratio of 2.5 and an ozone/CB ratio of 1.5 increased the conversion efficiencies 13.0 and 6.3 times, respectively, compared with photolysis alone. The relative humidities of the reaction media affected the target conversions, and also the dominant oxidizer in the conversion process (O-3 for EB and hydroxyl radicals for CB). Possible pathways and mechanisms were suggested on the basis of the intermediates identified, some of which were more soluble and biodegradable than the target compounds. Two kinetic models, based on initial concentration and ozone addition, were developed to describe the EB and CB conversion behaviors. The preliminary results indicated that ozone-assisted photodegradation enhanced gaseous EB and CB decomposition, and that this could be a promising technology for the conversion of recalcitrant and insoluble volatile organic compounds. (C) 2013 Elsevier B.V. All rights reserved.