A study on the photocatalytic degradation of methyl tertiary butyl ether (MTBE) vapor was performed with respect to reaction parameters, kinetics, and mechanism, A conventional TiO2-coated plate system was used for this initial work on vaporized MTBE. On irradiating with UVBLB (similar to 5 mW/cm(2)), 0.6 Mg/cm(2) of TiO2 (P25) photocatalyst showed the highest reaction rate (0.85 mumol/min) for 25.76 mumole of MTBE (1000 ppmv). The numerical values obtained depended predictably with respect to light intensity, initial concentration, and quantity of P25. The photocatalytic degradation of MTBE followed Lanmuir-Hinshelwood kinetics with a linearity of 0.989. As far as the mechanism of degradation is concerned, attack by generated hydroxyl radicals on the methoxy group in the MTBE structure dominated and proceeded through tert-butyl formate (TBF) as an intermediate, instead of methyl group to proceed through producing 2-methoxy-2-methyl propionaldehyde (MMP). TBF finally degrades to CO2 through acetone, which was shown easily converted to CO2. This study shows that the use of sunlight seems to be possible given adequate tools for concentrating the light. (C) 2003 Elsevier B.V. All rights reserved.