Master of Science in Engineering Science (MSES)
Nitrogen oxides (NOx) emitted from vehicle exhaust are associated with negative health impacts and are a precursor to ozone. Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can degrade pollutants such as NOx through heterogeneous photocatalysis. Although this technology has the potential to support environmentally friendly road infrastructure, a number of design and operational parameters may affect its effectiveness and thus need to be evaluated. The goal of this study was to measure the NOx reduction efficiencies from photocatalytic pavements under various environmental conditions common to highways. To achieve this goal, the objectives were to: (a) evaluate the influence of photocatalytic layer design and operating parameters on the efficiency of photocatalytic concrete pavement; (b) measure the impact of mixed pollutants on NOx reduction efficiency; and (c) measure the impact of roadway contaminants on NOx reduction. To achieve the first objective, the effects of relative humidity level, pollutants’ flow rate, and photocatalytic layer design parameters, including titanium dioxide (TiO2) percent content and aggregate sizes, were investigated. The environmental efficiency of the samples to remove NOx from the atmosphere was measured using a newly developed laboratory setup. The photocatalytic layer designs without fines achieved the highest photodegradation rates. In addition, the increase from 3% to 5% TiO2 resulted in minimal improvement to the NOx removal efficiency. To achieve the second objective, NOx reduction efficiencies were measured for various NO2/NOx ratios at various flow rates and humidity levels. Increasing the flow rate and NO2/NOx ratio negatively affects the effectiveness of the photocatalytic process. The highest photodegradation rate was observed at 25% relative humidity, which balances the availability of hydroxyl radicals at the surface with NOx contact with the photocatalytic surface. To achieve the third objective, three common roadway contaminants were tested - dirt, de-icing salt, and motor oil - at two contrasting coverage levels. The contaminants had a strong, negative impact on the photocatalytic NOx removal efficiency. The impact of contaminants’ coverage was largely dependent 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 NOx efficiencies.
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Dylla, Heather, "The effects of highway environmental conditions on photocatalytic pavement's ability to reduce nitrogen oxides" (2011). LSU Master's Theses. 240.