Nanosized titanium dioxide particle emission potential from a commercial indoor air purifier photocatalytic surface: A case study.

Background: Photocatalytic air purifiers based on nano-titanium dioxide (TiO 2 ) visible light activation provide an efficient solution for removing and degrading contaminants in air. The potential detachment of TiO 2 particles from the air purifier to indoor air could cause a safety concern. A TiO 2 release potential was measured for one commercially available photocatalytic air purifier "Gearbox Wivactive" to ensure a successful implementation of the photocatalytic air purifying technology. Methods: In this study, the TiO 2 release was studied under laboratory-simulated conditions from a  Gearbox Wivactive consisting of ceramic honeycombs coated with photocatalytic nitrogen doped TiO 2 particles. The TiO 2 particle release factor was measured in scalable units according to the photoactive surface area and volume flow (TiO 2 -ng/m 2 ×m 3 ). The impact of  Gearbox Wivactive on indoor concentration level under reasonable worst-case conditions was predicted by using the release factor and a well-mixed indoor aerosol model. Results: The instrumentation and experimental setup was not sufficiently sensitive to quantify the emissions from the photoactive surfaces. The upper limit for TiO 2 mass release was <185×10 -3 TiO 2 -ng/m 2 ×m 3 . Under realistic conditions the TiO 2 concentration level in a 20 m 3 room ventilated at rate of 0.5 1/h and containing two Gearbox Wivactive units resulted <20×10 -3 TiO 2 -ng/m 3 . Conclusions: The release potential was quantified for a photocatalytic surface in generalized units that can be used to calculate the emission potential for different photocatalytic surfaces used in various operational conditions. This study shows that the TiO 2 nanoparticle release potential was low in this case and the release does not cause relevant exposure as compared to proposed occupational exposure limit values for nanosized TiO 2 . The TiO 2 release risk was adequately controlled under reasonable worst-case operational conditions.