Light2CAT report D.5.3 Assessment of the air quality after the execution of the photocatalytic structures shows the final performance indicators and describes the major benefits obtained through the use of photcatalytic concretes in relation to geographical positions, irradiation conditions, influence of seasonal climatic variations, wind and air circulation.
At first glance D.5.3 highlights 56.5 % NOx reduction (from 84.0 to 36.5 ppb) in Valencia and 18.9 % NOx reduction (from 26.2 to 21.3 ppb) in Copenhagen. Along the motorway, abatement of total NOx was assessed around 10 % under favourable total solar irradiance conditions (>600W/m2 ).
When analysing the results more in details and in relation to the main project objectives, it can be noted that:
1. The very high difference in Valencia could be due to very different conditions for the measurements when the photocatalytic pavers were installed compared to the reference period: different weather due to different time of the year and also different traffic load. Most likely, the actual photocatalytic activity on the Spanish site is significantly overestimated.
2. In the city of Copenhagen, the total NOx concentration during the photocatalytic period seems to be constantly lower than the reference one. This independently on the concentration of UV light in the solar radiation reaching the surface. On the contrary, a previous study employing undoped TiO2 found that a threshold of ca. 2.5 % of UV fraction of total light irradiance at solar noon (corresponding to a total UV energy delivered to the surface equal to 600kJ/(m2 day)) was necessary to achieve a true photocatalytic effect.
3. In summer along the motorway, between sunrise and 9 am and between 4 pm and sunset, the Light2CAT was able to remove 12.64 % of NO and 7.37 % of NO2. This is hard to reconcile with photocatalytic activity promoted by UV photons only, as in this part of the day UV concentration is minimum.
Most importantly, the amount of NO2 (i.e. the most toxic and dangerous species amongst nitrogen oxides ordinarly present in the atmosphere) removed is unprecedentedly higher than what found in other existing reports related to the nitrogen oxides abatement capabilities of commercially available TiO2. This is the consequence of the greater selectivity towards nitrates exhibited by the Light2CAT photocatalyst when compared to ordinary TiO2.
This high selectivity is a major benefit for environmental remediation technologies. The catalyst works well in lowering the amount of NO2 in the air, and indirectly reducing the amount of ozone produced by NO2 photolysis and followed reaction with molecular oxygen. These benefits are not achievable with undoped TiO2, as its selectivity to nitrates is – often – not high enough.
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