New pollution eating paint will clean the air

A new form of paint that can absorb some of the noxious gases from vehicle exhausts goes on sale across Europe next month. Its manufacturers hope it will give architects and town planners a new weapon in the fight against pollution, an article in New Scientist reports.

The new product, Ecopaint, is designed to absorb nitrogen oxides, one of the causes of respiratory problems and smog production. Dr Robert McIntyre, of Millenium Chemicals who developed the paint, says a typical 0.3 millimetre layer would be enough to last five years in a heavily polluted city.

Its secret lies in spherical nano-particles of titanium dioxide and calcium carbonate. These are embedded in the paints base, polysiloxane, a silicon-based polymer. The base is porous enough to allow the nitrogen oxides to diffuse through it and adhere to the titanium dioxide particles.

These particles absorb ultraviolet radiation in sunlight and use this energy to convert nitrogen oxides to nitric acid. The acid is then either washed away in rain, or neutralised by the alkaline calcium carbonate particles, producing carbon dioxide, water and calcium nitrate.

Previous attempts to use titanium dioxide to break down nitrogen oxides failed because it attacked the base material as aggressively as it did the pollutants. The polysiloxane is resistant to this, although the developers admit that they don't know why.

Due to the nano-particles being so small, the paint is clear. Pigment can be added, however, and the first paint to go on sale will be white.

Ecopaint was developed by Millennium Chemicals under a European Union funded programme - the Photcatalytic Innovative Coverings Applications for Depollution Assessment programme (PICADA). The company says their experience with another catalytic coating shows how air quality can be improved.

In 2002, 7,000 square metres of road surface were covered with catalytic cement in Milan, Italy. Residents reported that it was noticeably easier to breathe and concentrations of nitrogen oxides at street level were cut by up to 60%.

EU Member States are required to monitor nitrogen oxide levels and ensure that by 2010 they have fallen below an annual average of 21 parts per billion.



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