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Field trials of photocatalytic pavements were recently initiated and are being considered by many states (e.g., Virginia, Texas, New York, and Missouri). Results from this study are from the country's first air-purifying asphalt and concrete photocatalytic pavements on December 20, 2010. The test area was a pavement site located on the Louisiana State University campus in Baton Rouge. The objective of this study was validation of photocatalytic degradation of nitrogen oxides (NOx) at the test site by measuring nitrate salts (NO3) deposited on the pavement surface. With quantification of the nitrate levels produced in the field attributable to photocatalytic activity, measurements were correlated to laboratory test results of NOx reduction efficiency. A field sampling procedure of NO3 deposited on the pavement surface is presented. On the basis of the results of the experimental program, the proposed method to quantify photocatalytic efficiency through nitrate measurements was successful. There was definite evidence that photocatalytic degradation of NOx was taking place in the treated section. In addition, the photocatalytic process was active during the first 4 days followed by a slight decrease in degradation of NOx. Full regeneration of photo catalytic activity took place through a self-cleaning process during a rain event. Six months of traffic and in-service operating conditions had negligible effects on the efficiency of the photocatalytic coating. In addition, there was good agreement between nitric oxide removal efficiency measured in the field after one day of nitrate accumulation and in the laboratory at the same relative humidity.

Numerous laboratory studies have demonstrated the ability of nano and ultrafine titanium dioxide (TiO2) photocatalytic pavements to trap and degrade nitrogen oxides in the air when irradiated with ultraviolet light. However, to understand better how photocatalytic pavements will perform under real-world conditions, field studies are necessary. Quantification of the reduction of nitrogen oxides (NOx) in field studies is difficult and challenging because of the many environmental and operating variables. The objective of this paper is to identify evidence of photocatalytic NOx reduction and to determine the environmental and operating factors that affect efficiencies under real-world conditions. A quarter-mile concrete roadway was sprayed with a photocatalytic coating in Baton Rouge, Louisiana. This section was the first field installation of TiO2 photocatalytic pavement in the United States. NOx concentrations were monitored for both the coated and uncoated sections simultaneously for 3 weeks during the spring season to measure photocatalytic degradation directly. Further, nitrates were collected from the coated and uncoated areas for evidence of photocatalytic NOx reduction. Results from both approaches show evidence of photocatalytic NOx reduction. Environmental factors with significant impact on photocatalytic efficiency include relative humidity, solar intensity, and wind speed and direction.

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