Intercomparison of secondary inorganic aerosol concentrations in the UK with predictions of the unified Danish Eulerian model

Nitrate and sulphate concentrations were measured over the period January 2002-December 2003 on daily basis at two stations in the UK: a rural site (Harwell) and an urban site (Belfast). The measurements were compared with model results obtained by using the Unified Danish Eulerian Model (UNI-DEM), which was run using both a coarse resolution grid (50 km x 50 km surface cells) and a fine resolution grid (10 km x 10 km surface cells). The results from the comparison show reasonably good agreement between concentrations measured at the two stations and calculated by the model. This is achieved despite the absence of aqueous phase sulphur oxidation chemistry in the model. The model results were also used to predict the spatial distributions of nitrate and sulphate concentrations in the UK which agree well with observations. The contribution of mainland European emission sources and that of UK sources to pollution levels in the UK was estimated. The relative proportions differ substantially across the UK with the imported contribution to UK sulphate and nitrate typically in the range 20-45% and 35-65% respectively.