Scientists have used the no-flying period caused by the ash cloud to show for the first time that airports are themselves significant causes of pollution. Although long suspected, the fact that mass take-offs and landings are large pollution sources could never be proved before, because aircraft pollution could not be measured as separate from the pollution caused by vehicles operating near by.
But an analysis of the first three days of the unprecedented closure of UK airspace, at Heathrow and Gatwick, shows that there is a definite air pollution caused by air traffic in the vicinity of airport hubs.
Pollution near both airports dropped significantly during the first three days of the shutdown. During last Thursday, Friday and Saturday, levels of two major pollutants, NO2 (nitrogen dioxide) and NOx (the generic term for oxides of nitrogen, taken together) fell virtually to zero.
Such nitrogen pollutants can exacerbate breathing difficulties in older people and those suffering from cardiac conditions, and can react with sunlight to form an even more damaging pollutant, ozone, which causes the sort of "urban smogs" seen in Los Angeles. NOx and NO2 are particularly associated with jet aircraft, as they are produced by the high-temperature mix of aviation with fuel.
The new analysis has been produced by Ben Barratt and Gary Fuller of the Environmental Research Group at King's College, London. The group said yesterday: "This period of unprecedented closure during unexceptional weather conditions has allowed us to demonstrate that the airports have a clear measurable effect on NO2 concentrations, and that this effect disappeared entirely during the period of closure, leading to a temporary but significant fall in pollutant concentrations adjacent to the airport perimeters."
"We have always been fairly confident that there was this 'airport effect' but we have never been able to show it," Dr Barratt commented. "The closure gave us the opportunity to look at it, and there is a very strong indication that it is the case."
The researchers are also going to study the pollution effects of the fall in airport motor traffic during the shutdown. Ed Dearnley, of Environmental Protection UK, which specialises in air quality campaigning, said yesterday: "This has been an excellent opportunity to find out exactly what the environmental impact of airports really is."