A detailed reaction-reactor model of the kinetics of dichloroacetic acid (DCA) degradation employing ozone with UVC radiation was developed. The description differentiates the existence of illuminated and dark sections of the reacting system, as well as shows the application of the differential concept of chemically active species radiation absorption coefficients and the ones corresponding to other components that only participate in the characterization of the total existing radiation field. A distinction is made between the mass balances for ozone (operating in a well-stirred, recirculating, continuous flow reactor) and all other intervening species (operating in a well mixed, recirculating batch reactor). Additionally, the conceptualization of the requirement of a fully irradiated photochemical reactor is applied in order to confer meaningfulness to the obtained kinetic parameters. The complete sequence presented here includes three parallel reactions: (i) direct photolysis, (ii) direct ozonation and (iii) ozonation plus UVC radiation. This study attempts to reach one single 31 steps sequence that, by suitable cancellation of the reaction paths that specifically do not take part in each of the corresponding processes, reproduces the kinetics of direct photolysis or direct ozonation without UV radiation. Three sets of ordinary differential equations resulting from the mass balances of each one of the three parallel reactions are reported. Upon estimation of the missing kinetic constants for DCA, simulation results always show good agreement with experimental data. Through a parametric sensitivity analysis, it has been shown that without loss of accuracy, the model can be safely reduced to just 23 steps. (C) 2011 Elsevier B.V. All rights reserved.