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

Delhi matches Beijing for air pollution threatening public health

Along with President Obama's state visit to India yesterday,  a number of news articles came with titles like "Obama is breathing world’s dirtiest air in New Delhi".

Such statement is presumably based on atmospheric particulate matter, which has impacts on climate and human health. Atmospheric aerosols affect the climate of the earth by changing the amount of incoming solar radiation and outgoing terrestrial long wave radiation retained in the earth's system. Particles smaller than 2.5 micrometers or PM2.5, tend to penetrate into the gas exchange regions of the lung (alveolus), and very small particles (< 100 nanometers) may pass through the lungs to affect other organs. Exposure of PM is associated with health effects such as asthma, lung cancer, cardiovascular disease, respiratory diseases, premature delivery, birth defects, and premature death.

In 2014, World Health Organization study finds Indian capital had dirtiest atmosphere of 1,600 cities around the world for PM2.5 particles. See the WHO Ambient (outdoor) air pollution database 2014 available at http://www.who.int/phe/health_topics/outdoorair/databases/cities/en/ and embedded below

Environment is one of the focuses during Obama’s India trip . Following the agreement in November with Chinese President for both countries to limit or cut carbon emissions, Obama is expected to meet with Indian Prime Minister to discuss topics such as educe greenhouse gas emissions and boost clean energy production. Currently, India heavily relies on fossil fuels as energy source, which has transformed New Delhi into the planet’s most polluted capital and made India the third biggest national emitter of greenhouse gases.

References and more to read: 

http://www.theguardian.com/world/2014/may/08/india-admits-delhi-matches-beijing-air-polllution-world-health-organisation-cities

http://globalnews.ca/news/1789010/obama-to-breathe-worlds-dirtiest-air-amid-climate-talks-in-new-delhi/