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 (TiO2) visible light activation provide an efficient solution for removing and degrading contaminants in air. The potential detachment of TiO2 particles from the air purifier to indoor air could cause a safety concern. A TiO2 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 TiO2 release was studied under laboratory-simulated conditions from a Gearbox Wivactive consisting of ceramic honeycombs coated with photocatalytic nitrogen doped TiO2 particles. The TiO2 particle release factor was measured in scalable units according to the photoactive surface area and volume flow (TiO2-ng/m2×m3). 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 TiO2 mass release was <185×10-3 TiO2-ng/m2×m3. Under realistic conditions the TiO2 concentration level in a 20 m3 room ventilated at rate of 0.5 1/h and containing two Gearbox Wivactive units resulted <20×10-3 TiO2-ng/m3.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 TiO2 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 TiO2. The TiO2 release risk was adequately controlled under reasonable worst-case operational conditions.