In German cities, toxic nitrogen oxide concentrations are exceeding maximum admitted levels, but this is about to change with the new innovative paving slabs reducing the amount of the nitrogen oxide in the air.
Because the quality of the ambient air is not always good in urban areas because of road traffic, which is one of the primary sources of these emissions, in the city of Fulda the officials made a leap forward in eliminating pollution.
On the Petersberger StraiÃ…Â¸e road, where the pollution level is 40 micrograms per cubic meter, some special slabs coated with titanium dioxide will convert the harmful substances such as nitrogen oxide into nitrates. Titanium dioxide uses sunlight to accelerate a chemical reaction which occurs naturally.
These paving slabs are developed by FC Ni¼dling Betonelemente. The Fraunhofer Institute for Molecular Biology and Applied Ecology IME in Schmallenberg, founded by the German Environment Foundation, provided proof of the effectiveness of the “green” slabs and the researchers also determined the risk it poses to the environment.
“Experiments in Italian cities had already shown that photocatalytic paving slabs can improve the air quality. We wanted to see if they would also be effective here in Germany, where we have lower levels of light intensity and fewer hours of sunshine. Of course, 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.” said Dr. Dr. Monika Herrchen, a scientist at the IME.
In the beginning, the concrete manufacturer FC Ni¼dling produced different samples, trying to test different surfaces and types of cement and titanium dioxide contents. They chose the standard commercial photocatalyctic cement, which is a cement that reacts to solar radiation. Herrchen said that they were “able to verify the effectiveness of the optimized slabs in a variety of tests.”
After the tests, where the researchers recorded degradation rates of 20 to 30 % in wind and ligh condition, and degradation rates up to 70% in the without wind conditions, for both nitrogen monoxide and nitrogen dioxide, Herrchen pointed out the benefits of the “green slabs”: “They also 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.”
Another benefit of the new innovative slabs is that the nitrate generated during the conversion process poses no risk to the environment. The nitrates are running off into the drainage system. After passing through the wastewater treatment plant, they end up on an agricultural field. This aspect is not harmful to the land, because the maximum permitted concentration of nitrate in groundwater is 50mg/l and the maximum nitrates traceable back to photocatalytic reaction is 5mg/l.
The measurement were taken at the height of three meters above the Gothaer Platz in Erfurt, which now is paved with Air Clean air cleaning slabs. Herrchen sums up: “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.”