A pair of "pollution radars" have been created by scientists to probe the city's air.

The two devices, being built at the University of Leicester, will sit atop the National Space Centre and the university, scanning the skies.

They will detect light from the sky and analyse it to decode what pollutants the sun's rays have passed through.

Having the scanners at different sites will allow the scientists to build up a three-dimensional model of polluted areas in the city.

That information could then be used to clean up the city's air.

The metre-tall devices, funded with the backing of East Midlands Development Agency and local companies, are the first of their kind.

Roland Leigh, from the university's Department of Physics, is leading the project. He said: "It's quite cutting edge equipment we're making here.

"We call it 'a radar', but it's actually collecting scattered sunlight into a spectrometer and analysing the light. With two of them looking in all directions you build up a three-dimensional map of Leicester's pollution.

"We hope to deploy them on the university and the National Space Centre in about September, and then get the measurements by the end of 2010.

"The map will show where the air quality issues are."

As well as showing where exhaust fumes and other pollutants are, it is hoped the results will reveal some interesting facts about how chemicals change in the air, turning into other gases such as nitrogen dioxide and ozone that can cause breathing difficulties and also damage crops grown on farms.

The university will pass its information on to Leicester City Council, which is responsible for tackling pollution.

While the issue is a priority, the situation in the UK has improved hugely since the 1980s, according to Dr Paul Monks, a chemistry lecturer at the University of Leicester and the new chairman of the Government's air quality advisory committee.

He said: "Since the Clean Air Act in the 1950s things have been improving all the time. "And since the 1980s pollution in Leicester has been reduced by two thirds thanks to things like cleaner power stations and cars.

"Pollution here in Leicester is certainly decreasing. And we also have some of the most advanced thinking on the subject going on here."