As well as the direct benefits to residents, who had days of unaccustomed peace from aircraft noise, there was an indirect environmental benefit from volcanic ash cloud.
The cessation of flights at major airports allowed scientists to confirm that airports are significant causes of air pollution.
Because the pollutants produced by aircraft and airport operations are largely the same as those produced by other sources, such as roads and buildings, it is not normally possible to measure the proportion of total concentrations of pollutants coming from the airport. (The proportion has to be estimated by complex computer simulations.)
Ben Barratt and Gary Fuller of the Environmental Research Group at King’s College, London carried out a study using air pollution data before and during the closure of Gatwick and Heathrow airports.
In outline, what the researchers did was to find two air pollution monitors, one upwind and one downwind of the airport during the closure. When the airport was working normally, the downwind monitor would record the pollution from the airport while the upwind monitor would not. But when the airport was closed, there would be no pollution from the airport at either monitor. By subtracting results, the researchers could calculate pollution caused by the airport and its planes.
Ben Barratt and Gary Fuller said “This period of unprecedented closure during unexceptional weather conditions has allowed us to demonstrate that the airports have a clear measurable effect on NO2 [nitrogen dioxide] 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 added “The closure gave us the opportunity to look at it, and there is a very strong indication that it is the case.”
At Gatwick, the concentrations of NO2 due to the airport at the monitoring point SW of the airport dropped from an average of 8ug/m-3 (microgrammes per cubic metre) to zero when the airport was closed. This would correspond to a drop in the annual average of pollution from all sources from about 18 to 16 ug/m-3. (The drop in annual average is much less because the monitor SW of the airport is only downwind for a smallish proportion of a year.)
At Heathrow, the concentrations of NO2 due to the airport at the monitoring point SW of to the airport dropped from an average of 19ug/m-3 to zero when the airport was closed. This would correspond to a drop in the annual average of pollution from all sources from about 33 to 30 ug/m-3 at point just SW of the airport.
For more information see short report (pdf, 4pp).