A smog-busting paint could soon be cleaning up air in polluted cities and making the place look cleaner too.

The new invention called Ecopaint cleans up the air by trapping noxious gasses from vehicle exhausts and neutralises the nitrogen oxides they contain.

The paint then flushes out the neutralised products when it next rains. The by-products are safe chemicals such as water, carbon dioxide and calcium nitrate.

According to New Scientist magazine the paint contains spherical nanoparticles of titanium dioxide and calcium carbonate 30 wide. Because the particles are so small, the paint is clear, but pigment can be added. The first paint to go on sale will be white. As the paint continues to break down the noxious city air it reaches a point where all the calcium carbonate is exhausted. At this point the paint starts to change colour.

In a typical paint layer, there will be enough calcium carbonate to last five years in a heavily polluted city, says the British company Millennium Chemicals, based in Grimsby, Lincolnshire, which developed the paint.

The paint goes on sale in March and the makers believe it will give architects and planners a new tool to fight pollution.

Trails of a similar process using a cement render in Milan were successful with residents reporting that it was noticeably easier to breathe. The concentration of nitrogen oxides at street level were cut by up to 60 per cent.