Within a pilot programme comprising several projects, the nitrogen oxide reduction potential of titanium dioxide was to be investigated under real conditions on various structures of highly frequented traffic routes. The presented study describes the work carried out on a barrier on the surface of which a TiO2 suspension was applied. The investigations took place on the A1 between the junctions Osnabrück-Nord and Osnabrück-Hafen. The investigated area covered a length of approx. 2 km. In this section, the 6-lane motorway is enclosed on both sides by a noise barrier, to which a suspension containing TiO2 was applied in an airless process over a length of 1 km on both sides in September 2011. The coated area is approx. 25,000 m2. A 1 km long section without suspension was used as a reference area during the investigation. Before the photocatalytic materials could be used, several preliminary investigations had to be carried out. These included, for example, model calculations and sound investigations to exclude the possibility that the TiO2 suspension selected for the noise barrier influences the acoustic properties of the open-porey wall material. In addition, various project-accompanying investigations were carried out, e.g. soil analyses, weathering of test specimens or nitrate balancing of the discharge water on the noise barrier. The main inspections showed NO2 reductions in the single-digit percentage range. The highest reduction rates were observed on the eastern side of the motorway, where the pollutants could probably remain on the photoactive wall for longer periods than on the western side due to the prevailing transverse flow. This observation is supported by the model calculations accompanying the project. The development of the reduction rates in connection with the weathering investigations during the years of measurement data acquisition suggests that photocatalytic suspensions sometimes take several months to burn themselves free and allow the active TiO2 particles to surface. The traffic-related impurities on the photoactive surfaces certainly also have a counterproductive effect in the vicinity of roads. Measurements with passive collectors at several distances from the motorway also show that a noise barrier already results in a significant reduction in the NO2 concentration in the immediate area behind the structure. However, this is not – as with photocatalysis – a degradation or conversion of the NO2, but only a transport of the pollutants into higher layers of air and dilution in clean air up there. (Author/publisher)
Samenvatting