Abstract
ABSTRACT 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).
Highlights
Engineered nanomaterials (ENM) can be released to the environment, including the atmosphere, during many instances throughout the product life cycle (Gottschalk et al, 2011)
In the presence of TiO2 nanoparticles, the NO2 reduction gradually increases with increasing ultraviolet A (UVA) exposure
The reduction increased from 35.7% to 63.2% by increasing the UVA exposure from 351.6 W s m–2 to 2109 W s m–2 with a reactive surface area concentration of 0.79 m2 m–3
Summary
Engineered nanomaterials (ENM) can be released to the environment, including the atmosphere, during many instances throughout the product life cycle (Gottschalk et al, 2011). They can be released into the air, e.g., with the flue gas from an industrial facility where they are produced or processed, during mechanical treatment of a composite with embedded ENM (e.g., sanding of a coating) or during waste incineration. Keller et al (2013) reported that 0.1–1.5% of produced ENM are estimated to be released into the atmosphere during their life cycle. ENM may interact with gaseous components of the air and affect atmospheric chemistry. Due to the generally high surface-area-to-mass ratio of ENM, even rather low mass concentrations of ENM may have a stronger effect on atmospheric chemistry than their larger counterparts
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