On the road to cleaner air

Nitrous oxides released by cars can now be reduced by the roads they travel on after scientists in the Netherlands develop a road surface that cleans the air.

Professor Jos Brouwers and researchers from the Einhoven University of Technology developed an air-purifying concrete which contains titanium oxide. This removes nitrogen oxides (NOx) from the air and converts it into harmless nitrates with the help of sunlight, which can be rinsed away by rain.

Researchers tested the effectiveness of the air-purifying concrete against normal paving stones in the municipality of Hengelo in the province of Gelderland. They took three air-purity measurements at heights of between half and one-and-a-half metres and found the area paved with air-purifying concrete had 25 to 45% lower levels of NOx than the regular concrete.

“The air-purifying properties of the new paving stones had already been shown in the laboratory, but these results now show that they also work outdoors,” said Brouwers, a professor of building materials in the department of architecture, building and planning.

The air-purifying concrete can also be mixed with open asphalt for roads where asphalt is required, and Brouwers’ estimates suggest the use of the concrete does not have a major impact on the cost of the road. Although the stones are 50% more expensive than normal concrete stones, the total road-building costs are only 10% higher.

The new concrete could be used in area when the levels of NOx are already above permitted levels, or in self-cleaning and air-purifying building walls. The concrete is able to break down algae and dirt so the structure would always remain clean.