Photocatalytic Elimination of Nitrogen Oxides (NOx), Ozone, BAP and Organic Pollutants from the Contaminated Air in Prague and Milan - 12 Months Field Study
Authors: Prochazka JAN 
Published: December 2024

Smart Cities start with clean air, clean water, clean look, pleasant environment and energy savings. Data collected in a 12 month field study clearly demonstrate that photocatalytic technology (i.e. FN NANO) is a convenient, energy and cost efficient solution to the air pollution problem. New methodology to determine the depollution efficiency of urban structures on 3D printed objects inside a "City reactor" will be presented.
Daylight energy activated photocatalytic surface shows a strong electron deficiency of 3.2eV (1), and have enough power to break down molecules of polluting compounds such as nitrogen oxides (2), ozone (3), organic volatile compounds, benzo-a-pyrene and other harmful pollutants.
UV + TiO2 → TiO2 (h + e−) 3,2eV (1)
NO (hv,TiO2)→(NO2)ads.+ H2O → NO3
− (2)
2O3 + hv → 3O2 (3)
Lab studies carried out over the past 15 years determine that facades painted with photocatalytic coating can easily compensate for emissions from the automobile traffic [1]. These lab data were confirmed by our long-term field study in real conditions of the polluted city of Prague (CR) and Milan (IT).
Initially, there was a question, if the street mixture of pollutants will degrade on the photocatalytic surface with the same rate as the individual compounds in the lab [2,3]. Our study shows that photocatalytic degradation of pollutants in the real environment is even more efficient than the ISO 22197 based lab measurements. The highest efficiency we could measure with real air was 80% elimination of NOx. More importantly, the long-term average (12 months/all seasons) indicates 42% DeNOx efficiency. This study clearly demonstrates that photocatalysis can be used as an inexpensive coating technology to improve the quality of air in polluted cities.
Our former studies showed high efficiency of the composite FN NANO coatings for removal of VOCs [4]. This was confirmed by measurements in the real conditions of the polluted cities of Prague and Milan. In addition, these studies demonstrated that concentrations of ozone are instantly converted into harmless molecules of oxygen on the photocatalytic surface [3]. The intensity of UV radiation determines the formation of ozone during the day, but the same radiation, in combination with the photocatalytic surface, is able to eliminate these ozone emissions. Relative air humidity does not impact the function of the photocatalytic coating in contrast to the layer of TiO2 photocatalytic standard Evonik P25 (Table 1). The initial concentration of ozone of 100 ppbv can be regularly found outdoors on sunny days.
Table 1 Photocatalytic removal of ozone

Relative humidity (%)

FN NANO2
Conversion (%)

P25
Conversion (%)

0

42

42

50

40

33

100

33

13

The photocatalytic surface not only cleans the air, but at the same time, it protects facades from UV radiation and soiling due to the self-cleaning properties of the photocatalytic coating. It prolongs facade life, and save money on maintenance and works as an giant air purifier.
Some of these coatings have a significant cooling effect, measured by the Cool Roof Council, suitable for cooling of the heat islands (cities).
Standard city model for prediction and mapping of spreading emissions was used to map disappearance of the nitrogen oxides pollutants. It provided valuable information on modeling and quantification of the street canyon photocatalytic air depollution. Over 10 % of elimination of pollutants was measured and can be expected in the street canyons [5].
All these effects are efficient, inexhaustible and long lasting, presenting a new standard in the urban architecture and environmental planning.
Keywords: FN NANO® photocatalytic coatings, self-cleaning coatings, decontamination, air cleaning, NOx, ozone, VOCs, BAP.
Acknowledgements. This project was realized with the financial support from the Ministry of Industry and Trade of the Czech Republic (TRIO FV 40209)
References
[1] R. Zouzelka, J. Rathousky, Photocatalytic abatement of NOx pollutants in the air using commercial functional coating with porous morphology, Appl. Catal. B Environ. 217 (2017) 466–476.
[2] Mikyskova, E., Martiniakova, I., Zouzelka, R. & Rathousky, J. (2022): Photocatalytic NOx abatement: The effect of high air-flow velocity, Environmental Technology & Innovation.
[3] Zouzelka, R., Martiniakova, I., Muzikova, M., Mikyskova, E., & Rathousky, J. (2022): Photocatalytic Abatement of Ozone, VOC and NOx Pollutants in the Air Stream, Journal of Industrial and Engineering Chemistry
[4] Namrata Pathaka, at el., Efficacy of photocatalysis and photolysis systems for the removal of ethylene under different storage conditions; Postharvest Biology and Technology 147 (2019) 68–77
[5] Nosek at el.,The role of flow structures in the effective removal of NOx pollutants by a TiO2-based coating in a street canyon; Journal of Environmental Chemical Engineering 11 (2023) 109758

Figure 1