This study was undertaken to evaluate the effect of photocatalytic treatment by ultraviolet (UV) irradiation of TiO2-coated ceramic filters on odorous compounds associated with livestock facilities. The removal efficiencies of four reduced sulphur compounds, 1-butanol, and four volatile fatty acids were evaluated in a photocatalytic reactor. Concentrations were measured using online proton-transferreaction mass spectrometry (PTR-MS). Four driving factors (initial concentration, air flow rate, relative humidity, and UV light intensity) were assessed based on odour removal efficiency. With the exception of H2S, all the odorous compounds were removed with above 80% efficiency at lower flow rates (<200 m(3) h(-1)) and different initial concentrations. The removal efficiencies were significantly reduced when the air flow rate was increased to 500 m(3) h(-1) or higher (P < 0.05). No significant differences in removal were found in any of the odorous compounds when relative humidity ranged from 40% to 80% at 20.1 +/- 1.4 degrees C. Thus pre-humidification of the TiO2 filter is not necessary. Furthermore, cutting the number of UV lamps by 50% did not reduce the removal efficiency of the odorous compounds, which demonstrated that energy consumption could be lowered without performance being compromised. Volatile by-products of each odorous compound were also investigated by PTR-MS and could be used to suggest possible reaction pathways. It has been demonstrated that PTR-MS is a useful tool for researching photocatalysis, and the results of this study can be used to optimise photocatalysis in the reduction of emissions of offensive odours in realistic conditions. (C) 2015 Elsevier B.V. All rights reserved.