A multi-annular photocatalytic reactor was designed, that shows good effectiveness for perchloroethylene (PCE) removal from contaminated air streams. In a previous work, a rigorous physical and mathematical model of the photocatalytic reactor was developed and experimentally verified. In this work, this mathematical model was used to study the radiative energy efficiency of the multi-annular photoreactor. The total quantum efficiency is defined as the ratio of the number of molecules of PCE reacted to the number of photons emitted by the lamp, and it is expressed as the product of the following factors: the reactor radiation incidence efficiency, the catalyst radiation absorption efficiency, and the overall reaction quantum efficiency. For the employed reactor, the numerical values of each one were 83%, 92%, and < 2.5%, respectively. Particularly, the dependence of the overall reaction quantum efficiency upon operating variables such as the PCE feed concentration, gas flow rate, irradiation level and relative air humidity was analyzed. These results are useful to optimize the operating conditions and design parameters of the photocatalytic reactor. (c) 2006 Elsevier Ltd. All rights reserved.