Nitrogen oxide reduction and nitrate measurements on TiO ₂ photocatalytic pervious concrete pavement

Photocatalytic compounds such as titanium dioxide (TiO ₂) can be used to construct pervious concrete pavements that can trap and degrade organic and inorganic particles in the air. Photocatalytic pervious pavements transform harmful pollutants such as nitrogen oxides (NO _x) into nitrates salts when subjected to UV light from the sun purifying ambient air from vehicle emissions. In spite of these benefits, an increase in nitrate levels may cause eutrophication. The objective of this study is to evaluate the amount of nitrates released due to pervious photocatalytic concrete and to assess potential eutrophication issues. To achieve this objective, pervious concrete samples were tested in the laboratory for photocatalytic NO _x reduction efficiency according to JIS standard. The test was performed using an innovative lab setup and conducted under different environmental and operational conditions including flow rate, UV intensity, temperature, and relative humidity. After testing, samples were washed with deionized water (DI) to collect the nitrates deposited on the surface. The concentration of nitrates collected was measured using a colorimetric method known as cadmium reduction. Results showed that photocatalytic pervious concrete is capable of purifying ambient air from NO _x. Results also showed that the concentrations of nitrate deposited on the surface are low and will not cause eutrophication problems.