Around the world, much of the energy policy debate centers on finding renewable technologies that can scale in order to make them cost-competitive with fossil-based fuels. This riddle is also paired with carbon’s effects on global warming. But there are other issues related to energy that fall under the radar, such as nitrogen oxide (NO and NO2, or NOx), which lingers in the air and presents a danger to public health.
Cities overrun by vehicle traffic suffer from high levels of NOx. In the US, where clean air legislation and improved technology made terms like “acid rain” as antiquated as the 1980s, NOx is still an problem. Other cities around the world struggle with high levels of NOx that make breathing unbearable. So while it is may be best to tackle problems from pollution at their source, workarounds are definitely needed. Researchers at Eindhoven University of Technology in the Netherlands evaluated a paving material that consumes those pesky NOx particles, and converts them into a benign nitrate that can simply wash away.
Professor Jos Brouwers and his team tested a concrete material coated with titanium dioxide(TiO2). TiO2 is a photocatalytic compound—which means in plain old English that the rest of us speak, it consumes the NOx that vehicles spew out, and by working with natural sunlight, transforms them into nitrates.
Brouwers’ crew tested the TiO2-coated concrete in the eastern Dutch city Hengelo. Two years ago they installed the material one of Hengelo’s busy streets that is narrow and lined with multi-level buildings. The researchers wanted to test an area that shoulders high level of traffic where emissions would linger, trapped by tall structures. The results after two years showed that the TiO2-lined pavement reduced levels of NOx particles by about 50%.
Some would question whether replacing one harmful toxin with nitrates, which can cause excessive algae growth, is simply replacing one problem with another. But according to Götz Hüsken, the inventor of this pavement who worked with Eindhoven University, NOx is by far more harmful—and washing the resultant nitrates away floats them to sewage treatment plants that already cope with nitrates.
Should municipalities rush out and rip out their sidewalks? Not so fast. This newfangled concrete right now costs about 50% more than your standard concrete; then again, labor and construction costs would remain the same, so the cost difference then narrows. Titanium dioxide, which is now used in many pigments for industrial use (and in toiletries as a sunblock), may also be a carcinogen, though such studies are all over the map.
The best bet for such a building material would be in cities that are highly polluted and choked by traffic. While not a panacea, it could help such cities buy time as they become more congested. More studies like those of Eindhoven University should continue as well—the success of their study shows that innovation is a factor that is crucial if we are to improve the air we breathe.
If this became a tried, tested, and trusted method, would the extra cost be worth it?