Effects of roadway contaminants on titanium dioxide photodegradation of nitrogen oxides

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Nitrogen oxides (NO x) emitted from vehicle exhaust are associated with negative health impacts and are a precursor to ozone production. Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can degrade pollutants such as NO x through heterogeneous photocatalysis. Photocatalytic layers include titanium dioxide nanoparticles that can trap and degrade organic and inorganic particles in the air and thus remove harmful gases from the air in the presence of ultraviolet light (sunlight). In addition, their superhydrophilic properties allow them to self-clean in the presence of rain. Although this technology has the potential to support environmentally friendly road infrastructure, the impacts of a number of design and operational parameters on the technology's effectiveness need to be evaluated before full-scale implementation. The objective of this study was to measure the impact of common roadway contaminants on the effectiveness of the ability of photocatalytic roadways to remove NO x from the atmosphere. Three common roadway contaminants were tested-dirt, deicing salt, and motor oil-at two contrasting coverage levels. Results of the experimental program showed that the three contaminant types had a strong negative impact on the photocatalytic NO x removal efficiency. The impact of the coverage of contaminants largely depended on the soilure type, with oil having the largest negative impact. An increase in the flow rate and air relative humidity also resulted in lower NO x efficiencies.

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Transportation Research Record

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