Quantification of air quality impacts of London Heathrow Airport (UK) from 2005 to 2012

Among other emission sources in the Greater London area, the international airport of Heathrow is recognised to be a major source of air pollution and is one of the UK locations where European air quality Limit Values are currently breached. However it is very difficult to differentiate between pollutants arising from airport operations and those from the large volumes of road traffic generated by the airport, as well as the nearby M4 and M25 motorways, A4 and A30 major roads, the conurbation of London and other external sources. In this study, eight years (January 2005-December 2012) of measurements of various air pollutants (NO, NO<inf>2</inf>, NO<inf>x</inf>, O<inf>3</inf>, CO, PM<inf>10</inf> and PM<inf>2.5</inf>) were investigated from 10 sites: eight sites are located within a distance of 2.5 km from the airport, while two sites representative of the regional background and of background air quality in London (Harwell (60 km WNW) and North Kensington (17 km ENE), respectively) were included. A series of statistical tools was thus applied to: (1) investigate the time series by analysing hourly data as diurnal, weekly, seasonal and annual patterns; (2) reveal the effects of the atmospheric circulation upon air pollution by analysing background-corrected polar plots and (3) quantify the impact of the airport upon air quality in the local area using the inter-site differences of measured concentrations. The results show different diurnal patterns in emissions of NO<inf>x</inf> from the airport and from the motorways. The concentration increment arising from passage of air across the airport during airport activity (6 am-10 pm) and with wind speed > 3 m s^-1 is ca. 1-9 μg m^-3 of NO<inf>2</inf> and 2-20 μg m^-3 of NO<inf>x</inf> at background stations. Such results are slightly lower than in a previous study analysing the 2001-2004 period. Air quality impacts of the M25 and M4 motorways are substantial only at the Hillingdon site (30 m from M4). Concentration increments of particulate matter can take either small positive or negative values.