A German city is installing paving slabs that scrub the air clean of pollutants.
The concentration of toxic nitrogen oxides in German cities regularly overtops permitted levels. But the city of Fulda is laying special paving slabs the length of Petersberger Strasse which promise to drastically reduce the amount.
The slabs are coated with titanium dioxide (TiO2), a photocatalyst which converts harmful substances such as nitrogen oxides into nitrates.
The Air Clean slabs were developed by FC Nüdling Betonelemente, and tested by the Fraunhofer Institute for Molecular Biology and Applied Ecology (IME).
Dr Monika Herrchen, a scientist at the IME, says, "The more intense the sunshine, the quicker the degradation of harmful substances, so our aim was to identify the formula with the highest photocatalytic efficiency rating."
The team produced a range of sample slabs incorporating different surfaces, colors, types of cement and TiO2 contents to develop the most effective formula.
Herrchen and her team recorded a drop in nitrogen oxide levels of 20 to 30 percent in specially-created street canyons. The measurements were taken at a height of three meters above the photocatalytic slabs, in variable wind and light conditions. When the wind was still, both nitrogen monoxide and nitrogen dioxide fell by as much as 70 percent.
The slabs remain stable over the long term. "Measurements recorded from 14 to 23 months after they were laid revealed no change from the initial degradation capability," says Herrchen.
The nitrate generated during the conversion process poses no risk to the environment, she says, simply running off into the drainage system, where it would be well below permitted levels.
"All in all, it’s possible to say that Air Clean significantly improves the air quality within a short space of time, and thus helps protect the environment," says Herrchen.