Purifying urban air with pavement containing titanium dioxide

A recent study published in the journal of Atmospheric Environment by Folli et al. demonstrated the effectiveness of cleaning NOx in urban air via photocatalytic oxidation using titanium dioxide as semiconductor photocatalyst added to pavement.

(source of image: www.mapfre.com)

The advantage of such technology is that photocatalystic oxidation only requires sunlight, existing oxygen and water in air. Therefore, remediation is continuous in day light.

In this study, researchers conducted a year-long field test in the city of Copenhagen. They employed two continuous air monitoring stations, one in the area with photocatalytic concrete pavers and the second one in the area without photocatalytic concrete and assessed the effectiveness of TiO2 containing pavement in removing NOx in the air.

The study indicates that a monthly abatement of NO was around 22% in the summer months;
NO noon abatement was >45% at the summer solstice, which corresponded to NOx noon abatement > 30%.

Personally, I think such technology is very promising although more research work needs to be done. Research questions worth to be addressed include but not limited to

• Does the technology also has the benefit of degrade other toxic chemicals in urban air such as polycyclic aromatic compounds?

• What's the over all benefit of such technology if widely used in urban pavement and building walls and how does the benefit of removal toxic chemicals compared to the cost. 

• What degradation products can be generated and how do they affect urban air and environmental quality? 

 In addition to the article by Folli et al. mentioned above http://dx.doi.org/10.1016/j.atmosenv.2015.02.025, the following articles on the removal of pollutants by adding TiO2 in cement are also informative on this topic.

• Folli, J.Z. Bloh, M. Strøm, T. Pilegaard Madsen, T. Henriksen, D.E. Macphee Efficiency of solar-light-driven TiO2 photocatalysis at different latitudes and seasons. Where and when does TiO2 really work? J. Phys. Chem. Lett., 5 (5) (2014), pp. 830–832 http://dx.doi.org/10.1021/jz402704n

• J. Ângelo, L. Andrade, L.M. Madeira, A. Mendes An overview of photocatalysis phenomena applied to NOx abatement J. Environ. Manag., 129 (2013), pp. 522–539 http://dx.doi.org/10.1016/j.jenvman.2013.08.006

• M.M. Ballari, H.J.H. Brouwers Full scale demonstration of air-purifying pavement J. Hazard. Mater., 254–255 (2) (2013), pp. 406–414 URL http://dx.doi.org/10.1016/j.jhazmat.2013.02.012