Demonstration project of air-purifying pavement in Hengelo, The Netherlands

MARÍA DE LOS MILAGROS BALLARI; JOS H.J.H. BROUWERS

Bordeaux

Simposio; European Symposium on Photocatalysis, (JEP 2011); 2011

European Photocatalysis Federation

Experiments concerning a full-scale demonstration of air purifying pavement in Hengelo (Ov.), The Netherlands, were performed. The pavement consists of concrete pavers, the top layer provided with a photocatalyst (TiO2) which is able, under the influence of light, to convert gaseous NOx (NO and NO2) into solid nitrates. Part of the photocatalysts were mixed-in in the concrete, the other part was applied as a coating. The full width of the street (about 5 m) in Hengelo was provided with this pavement over a length of 150 m (“DeNOx street”). Another part of the street, about 100 m, was paved with normal paving stones (“Control street”). The traffic intensity, and the orientation and lay-out (including adjacent houses), of both streets are practically identical. During 25 days measurements were done, from early in the morning till late afternoon. Measured parameters included traffic intensity, NO, NO2 and ozone concentrations, temperature and relative humidity, wind speed and direction, and the visible and UV light irradiance. Measurements were done before the street modification, after the street modification, and after the application of two coatings. NO and NO2 concentrations were simultaneously measured in both streets using two calibrated chemiluminescence NOx analyzers. Prior and parallel to these field measurements, the used stones were also measured in the lab according to ISO 22197-1:2007 to assess their performance. The following main conclusions could be drawn during the project execution: a) Originally the pavement was applied with stones containing relatively little photocatalytic powder, and the NOx reducing effectiveness was poor (at lab scale and at street scale). After the application of the coatings the effectiveness was high, but this decreased in time. b) A clear and direct relation between the NOx abating ability of a stone in the lab and in the street could be observed.  And this NOx reducing ability is directly related to the amount of photocatalyst present on the surface of the stone. c) Just after the applications of the photocatalytic coatings the NOx concentrations were, on average, 19% (considering the whole day) and 28% (considering only afternoons) lower than the obtained values in the control street. Under ideal weather conditions (radiation and relative humidity) in Summer time, a NOx concentration decreased of 45% could be observed (Figure 1b). d) The measurements were done at heights of 5 cm, 30 cm and 150 cm, and the NOx reduction at a height of 5 cm was about 1/3 higher than at 150 cm.