A NEW runway at Heathrow is a more likely prospect after a government study found the air pollution problem around the airport was less serious than had been feared and could be overcome.

Ministers are supporting a third runway and a sixth terminal at Heathrow to allow an extra 175,000 flights a year. The runway, 1.2 miles (2,000m), and capable of handling short-haul aircraft such as the Boeing 737 and the Airbus A320, would open between 2015 and 2020.

The 2003 aviation White Paper said that expansion could not go ahead if it would cause air quality to fall below the European Union’s minimum standard.

Department for Transport research had found previously that a third runway would expose 35,000 people living in the area to excessive levels of nitrogen dioxide. It is emitted by aircraft and vehicle engines and can cause fatal lung damage.

The new study contains results from 18 monitoring sites around Heathrow and shows that all but two were within EU limits in 2004. It also reports a small but significant downward trend in levels of nitrogen dioxide and says that nitrogen oxides and particulates are either falling rapidly or are already too low to present a problem.

The study, conducted by a panel of senior scientists, establishes a more accurate method of predicting how levels of air pollutants will change under various scenarios. The department will use the research to make recommendations on how nitrogen dioxide can be reduced sufficiently to allow a third runway to be built.

The Government has said it will make a final decision by next summer.

Ian Poll, Professor of Aerospace Engineering at Cranfield University, who was appointed to check the validity of the study, said: “The problem of air pollution is manageable and the continued expansion of Heathrow is desirable and technologically feasible.

“This report gives us a far better understanding of air quality issues and will stand up to the toughest scrutiny.”

Radical measures might be needed to reduce nitrogen dioxide to the required levels but there were no insurmountable problems, Professor Poll said.

The next generation of aircraft engines will produce far less nitrogen dioxide than those flying today.

Lord Soley, chairman of Future Heathrow, which campaigns for the airport’s expansion, said that the main source of nitrogen dioxide around the airport was from cars on the M4 and the airport’s access roads. A previous government study considered building a roof over a four-mile stretch of the M4 and installing vents to filter out nitrogen dioxide.

Lord Soley said that emissions could also be reduced near the airport by moving most of its 40,000 parking spaces to derelict land north of the M4 beside the M25. A new monorail line would link the new car park to the terminals.

John Stewart, chairman of ClearSkies, which represents people living under Heathrow’s flight paths, said: “It looks like the third runway will pass the air pollution test but there will still be the problem of a new flight path blighting 150,000 residents.”

Mr Stewart welcomed the Government’s decision, announced yesterday, to abandon plans to remove the cap on the number of night flights at Stansted, Gatwick and Heathrow. “It will be a great relief for residents to have Heathrow’s cap of 16 flights a night maintained. But I suspect this means ministers have decided to focus on the bigger battle of building a third runway,” he said.

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