We have received many enquiries asking what the effects of the closure of UK airspace has had on air quality surrounding major airports. In response we have made an initial analysis of NOX and NO2 concentrations surrounding Gatwick and Heathrow airports during the first three days of closure – Thursday 15th to Saturday 17th April 2010. This period was chosen due to the stable weather conditions with light north easterly winds, allowing a cross-sectional analysis upwind and downwind of the airports.
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.
Concentrations recorded by a monitoring site arise from a mix of pollution sources both local and distant affecting that specific location. In order to separate and quantify the affects of a particular local source, such as emissions from an airport, a control dataset is required. In this case pairs of monitoring sites were used located either side of each airport. The upwind monitors provided the control data. By subtracting hourly mean concentrations recorded by the upwind site from those recorded by the downwind site, an estimation of emissions from the airport could be made – termed ‘airport’ concentrations.
The figure above shows daily diurnal mean ‘airport’ NOX concentrations for the ‘open’ and ‘closed’ periods at a monitoring site close to the perimeter of Gatwick airport. The yellow shaded areas indicate hours where winds were from the north or north east during the closure period, i.e., the site was downwind of the airport runway. The chart shows that during normal operating conditions ‘airport’ NOX concentrations increase during the day peaking at around 22 to 25 µg m-3 on average. During the period of closure (15th to 17th April 2010) mean ‘airport’ NOX concentrations were zero most of the time. All concentrations were well below the lower 95% confidence interval indicating that the difference from ‘normal’ operation was statistically significant.
The analysis was repeated for NO2, with similar results. The annual mean NO2 concentration measured at this location (‘RG3’), to the south west of the airport, during 2009 would decrease from 18 µg m-3 to approximately 16 µg m-3 in the absence of airport emissions. The impact of the airport is likely to be greater in the populated areas to the north east of the airport (Horley) due to prevailing winds from the south west.
A similar analysis was carried out using a pair of monitoring sites surrounding Heathrow airport. ‘Airport’ NO2 concentrations were higher those at Gatwick and dropped from 27 µg m-3 to 8 µg m-3 during the closure period.
This exceptional closure has allowed us to demonstrate the impacts of airport emissions on their immediate neighbourhood. This preliminary study did not consider the impact of decreased traffic flows on airport feeder roads. Decreased flows are likely to have a significant effect on concentrations of vehicle-related pollutants close to such roads. Unfortunately, we do not have sufficient traffic data to carry out this analysis at this time.
A full version of the report is available for download using the link below.

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Item date 20/04/2010