A short-term intervention study — Impact of airport closure due to the eruption of Eyjafjallajökull on near-field air quality

The eruption of the Icelandic volcano Eyjafjallajökull in April 2010 resulted in an unprecedented flight-ban at many European airports for many days. While much of the scientific interest in the eruption was related to the chemical and physical properties of the ash cloud and how it dispersed, a secondary effect was the reduction in aviation emissions at airports around Europe and elsewhere. In this study we aim to quantify the impact the flight-ban had on concentrations of nitrogen oxides at measurement sites close to London Heathrow Airport. A technique based on boosted regression trees is used to build an explanatory model of NOx and NO2 concentrations based on hourly meteorological and aircraft emissions data in the 3-years preceding the flight-ban. We show that the airport closure resulted in an unambiguous effect on NOx and NO2 concentrations close to the airport, even though the ban only lasted six days. Furthermore, we estimate the annual impact airport emissions have on mean concentrations of NOx and NO2 for different years and compare these estimates with a detailed dispersion modelling study and previous work that was based on the analysis of monitoring site data. For the receptor most affected by the flight-ban approximately 200 m south of the airport we estimate the airport contributes about 13.5 μg m−3 NOx (≈23% of the total measured NOx concentration), which is similar in magnitude to detailed dispersion modelling estimates of 12.0 μg m−3, but approximately twice that of other estimates based on the analysis of ambient measurements. Other measurement sites showed more mixed results due to the prevailing meteorology at the time of the ban, which affected the extent to which these sites were affected by the flight-ban. The techniques developed and applied in this paper would have application to other short-term interventions that affect air quality.