People will be able to see how polluted Oxford's air is on a giant display screen, being dubbed a 'smokescreen'.

Modelled on the real time information displays found in some bus stops, up-to-the-minute readings of nitrogen dioxide levels will be put up in lights for all to see.

It will show how bad the air is in St Aldate's, High Street, Queen Street and St Ebbe's, taking readings from a series of monitoring stations dotted around the city.

Green campaigners hope that by displaying pollution levels the issue will climb to the top of the political agenda, heralding the introduction of a low emission zone (LEZ), where all but the greenest of vehicles would be banned from the city centre.

The first LEZ in the country recently started operating in London.

Although £7,000 has been set aside for the project, no final design or site has been chosen, but it could be mounted on the side of the Victorian, Grade-II* listed town hall, in St Aldate's, and would be broadly similar to our graphic, above.

European directives state that nitrogen dioxide levels - the main pollutant found in UK high streets - should not exceed 40 microgrammes per cubic metre.

However, the average reading in 2006 in Queen Street was 101, and in High Street it varied between 83 and 100, and, in 2005, a reading of 246 was recorded in St Aldate's.

Funding for the display was allocated after the Greens reached an agreement at Monday's city council budget meeting, where the sign was called a "smoke screen".

City Green group leader Craig Simmons said: "We have pollution monitors in the city centre constantly recording air quality levels.

"We felt it would be good to have a sign to make people aware of air quality and help to inform people.

"We do breach national and European limits at certain times of the year in certain parts of the city.

"The question is whether Oxford is any worse off than other cities - probably not.

"But for us that is not an argument - and it is certainly not an argument for people suffering with respiratory problems. This will stop the issue of air quality falling below the radar and better educate people."

Organisations, ranging from Calor Gas to the Chartered Society of Physiotherapists, have branded Oxford's air as among the dirtiest in the country.

City environmental health officer Tony Payne said: "The display will be something that gives data on the state of air quality in Oxford.

"Air quality fluctuates and it's still not conforming to European standards in some parts of the city "If air quality is not meeting directive levels that is the pre-cursor for having an air quality action plan - and the primary focus of that is to bring in a low emission zone.

"A certain amount of work has been done on that already."