Pollution-eating paint to help cities breathe

A paint that soaks up some of the most noxious gases from vehicle exhausts goes on sale in Europe next month.

Its makers hope it will give architects and town planners a new weapon in the fight against pollution.

Called Ecopaint, the substance is designed to reduce levels of the nitrogen oxides which cause respiratory problems and trigger smog production.

Patents were filed last week. The first paint to go on sale will be white.

Robert McIntyre of the British company Millennium Chemicals, based in Grimsby, Lincolnshire, which developed the paint, said the breakthrough was finding a robust base material.

Previous attempts to use titanium dioxide in paints to break down pollution faltered because it attacked the base material as aggressively as it did the pollutants. Polysiloxane is resistant to attack by titanium dioxide, though the developers are not yet sure why.

When the carbonate has been exhausted, the titanium dioxide will continue to break down nitrogen oxides, but the acid this produces will discolour the paint.

The paint-makers say that in a typical 0.3mm layer, there will be enough calcium carbonate to last five years in a heavily polluted city.

Ecopaint is being lab-tested as part of the Europe-funded Photocatalytic Innovative Coverings Applications for Depollution Assessment programme.

It has yet to be put to the test in the field, but the companies say their experience with another catalytic coating shows how air quality can be improved.

In 2002, after 7000sq m of road surface in Milan, Italy, were covered with a catalytic cement, residents reported that it was noticeably easier to breathe. The concentration of nitrogen oxides was at street level cut by up to 60 per cent.

Dimitrios Kotzias, who runs the programme's testing at the EU's Joint Research Centre in Ispra, Italy, says that the coating is effective because air turbulence is constantly carrying the gases over the surface, yet molecules stick to the surface long enough for the oxidation reaction to break them down.

Every building and piece of street furniture could be painted with it. Photocatalytic cements and paving slabs are already used in Japan, where the market for such building materials is growing.

And 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.

But current levels in cities are often tens of times that.

Painting out fumes

* The pollution-soaking paint has a porous base of Polysiloxane, a silicon-based polymer, containing tiny spherical particles of titanium dioxide and calcium carbonate.

* Polluting gases diffuse through the base and stick to the titanium dioxide particles. The particles absorb ultraviolet radiation in sunlight and use this energy to convert the gases to nitric acid.

* The acid either washes away in rain, or is neutralised by the alkaline calcium carbonate particles, producing harmless quantities of carbon dioxide, water and calcium nitrate, which also washes away.

- INDEPENDENT