Researchers at Eindhoven University of Technology in the Netherlands have developed a special concrete that can reduce the amount of nitrogen oxide air pollution by as much as 45 percent, according to a study published last month in the Journal of Hazardous Materials. The "photocatalytic" concrete is sprayed with titanium dioxide, a substance used in sunscreen because it blocks ultraviolet light. When mixed with concrete, it is able to break down nitrogen oxide, a pollutant emitted by cars and trucks.