In 2010, scientists at Eindoven University of Technology sprayed titanium oxide onto 1,000 meters of sidewalk in Hengelo, Netherlands. Because it is a photocatalytic material, the substance used sunlight to convert nitrogen oxide—in other words, the polluted air that was hovering over the sidewalk—into a harmless nitrate that was simply washed away by a later rainstorm.
So why isn't every sidewalk in every corner of the globe not coated with titanium oxide? Well, like most public work projects, it all comes down to cost. Right now, the material is around 50 percent more expensive than normal concrete, but it's expected that the price will eventually drop.
Photo: Science Direct/Los Angeles Times