Source apportionment of speciated PM10 in the United Kingdom in 2008: Episodes and annual averages

Abstract The Lagrangian atmospheric dispersion modelNAME (Numerical Atmospheric-dispersion ModellingEnvironment), has been used to simulate the formation and transport of PM 10 over North-West Europe in 2008. The model has been evaluated against UK measurement data and been shown to adequately represent the observed PM 10 at rural and urban sites on a daily basis. The Lagrangian nature of the model allows information on the origin of pollutants (and hence their secondary products) to be retained to allow attribution of pollutants at receptor sites back to their sources. This source apportionmenttechnique has been employed to determine whether the different components of the modelled PM 10 have originated from UK, shipping, European (excluding the UK) or background sources. For the first time this has been done to evaluate the composition during periods of elevated PM 10 as well as the annual average composition. The episode data were determined by selecting the model data for each hour when the corresponding measurement data was >50 μg/m 3 . All the modelled sites show an increase in European pollution contribution and a decrease in the background contribution in the episode case compared to the annual average. The European contribution is greatest in southern and eastern parts of the UK and decreases moving northwards and westwards. Analysis of the speciated attribution data over the selected sites reveals that for 2008, as an annual average, the top three contributors to total PM 10 are UK primary PM 10 (17–25%), UK origin nitrate aerosol (18–21%) and background PM 10 (11–16%). Under episode conditions the top three contributors to modelled PM 10 are UK origin nitrate aerosol (12–33%), European origin nitrate aerosol (11–19%) and UK primary PM 10 (12–18%).