Investigation of the Effect of Aerosolized TiO2 Nanoparticles on the NO2 Concentrations under UVA Exposure

Engineered nanomaterials (ENM) are utilized and produced during many engineering processes. However, they may generate airborne nanoparticles during different phases of their life cycles. TiO2, which is known for its photocatalytic properties, especially in terms of degrading NO2, is one of the most widely produced ENM. Ambient NO2 stems mainly from vehicular and industrial combustion processes and potentially harms human health upon inhalation. This study investigated the photocatalytic reduction of NO2 due to varying concentrations of aerosolized TiO2 nanoparticles during varying levels of ultraviolet A (UVA) exposure. Additionally, we evaluated the effects of low (5%), moderate (35%), and high (70%) relative humidity. Our results demonstrated that the decrease in NO2 depended on both the TiO2 concentration and the UVA intensity. However, when the former was high (> 3.23E+06 cm–3), the contribution of the latter was negligible. On the other hand, when the latter was high, the influence of the former was minimal. Furthermore, as the UVA exposure increased in duration, its effect became dominant over that of the TiO2 concentration. Finally, we found the relative humidity to be an insignificant factor during conditions with strong UVA (6328 W s m–2).