Sources of Submicrometre Particles Near a Major International Airport
Atmospheric Chemistry and Physics Discussions
Major airports are often located within or close to large cities; their impacts on the deterioration of air quality at ground level are amply recognised. The international airport of Heathrow is a major source of nitrogen oxides in the Greater London area, but its contribution to the levels of submicrometre particles is unknown, and is the objective of this study. Two sampling campaigns were carried out during warm and cold seasons at a site close to the airfield (1.2&thinsp;km). Size
... nsp;km). Size spectra were largely dominated by ultrafine particles: nucleation particles (<&thinsp;30&thinsp;nm) were found to be ~&thinsp;10 times higher than those commonly measured in urban background environments of London. A set of chemometric tools was used to discern the pollution arising from aircraft operations and those from other sources within the city or from the traffic generated by the airport. Five clusters and 6 factors were identified by applying <i>k</i>-means cluster analysis and positive matrix factorization (PMF) respectively to particle number size distributions; their interpretation was based on their modal structures, wind directionality, diurnal patterns, road and airport traffic volumes and on the relationship with weather and other air pollutants. Airport emissions, fresh and aged road traffic, urban accumulation mode and two secondary sources were then identified and apportioned. The comparison of cluster and PMF analyses allowed extraction of further information. The analysis of a strong regional nucleation event was also performed to detect its effect upon concentrations. The fingerprint of Heathrow has a characteristic modal structure peaking at <&thinsp;20&thinsp;nm and accounts for 30&ndash;35&thinsp;% of total particles in both the seasons. Other main contributors are fresh (24&ndash;36&thinsp;%) and aged (16&ndash;21&thinsp;%) road traffic emissions and urban accumulation from London (around 10&thinsp;%). Secondary sources accounted for less than 6&thinsp;% in number concentrations but for more than 50&thinsp;% in volume concentration. In 2016, the UK government provisionally approved the construction of a third runway; therefore the direct and indirect impact of Heathrow on local air quality is expected to increase unless mitigation strategies are applied successfully.