The enhancement effect of using TiO2 immobilized on activated carbon (TiO2/AC) filter for removing indoor air pollutant at parts-per=billion (ppb) levels has been previously reported. To further evaluate the TiO2/AC filter for practical application, it was installed in an air cleaner available in the commercial market and tested inside an environmental chamber. Nitrogen oxide (NO) and toluene were selected as target pollutant. Results showed that a higher removal efficiency of NO was achieved using shorter wavelength ultraviolet lamp than longer wavelength ultraviolet lamp. A higher NO removal was achieved using TiO2/AC filter compared to TiO2 filter only. The intermediate, NO2, generated from the photodegradation of NO was also successfully suppressed from exiting the system using TiO2/AC filter. A 25% higher of nitrogen oxides (NO,) was achieved using TiO2/AC filter compared to the TiO2/AC only. The higher removal efficiency of using TiO2/AC is owing to the large adsorption capacity provided by the activated carbon. The adsorbed NO is then transferred to the TiO2 for photodegradation. The difference in toluene removal efficiency using TiO2/AC filter compared to the TiO2 filter is even more significant. (C) 2004 Elsevier Ltd. All rights reserved.