Quantification of Reduction of Nitrogen Oxides by Nitrate Accumulation on Titanium Dioxide Photocatalytic Concrete Pavement

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 (NO_x) 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 NO_x 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 NO_x 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 NO_x. 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.