Application of the EMEP unified model to the UK with a horizontal resolution of 5 × 5 km²

The EMEP Unified model (Simpson et al. 2003; http://www.emep.int) is an Eulerian model that is driven by real-time meteorology. The model is applied over Europe for multiple years on a 50 × 50 km² grid, with meteorological fields updated every 3 h. While comparisons with measurements have shown generally robust performance of the EMEP model on a European scale (e.g. Simpson et al. 2006), pollutants such as reactive nitrogen and sulphur have a high spatial variability in their emissions and a short life time. Therefore, the associated dry deposition also has a high spatial variability (Vieno 2006; van Pul et al. 2008, this volume). This is very important when critical loads of nitrogen are calculated for specific ecosystems. For this reason a number of models have been developed for high resolution operation at a national scale. To address these issues for the UK, the EMEP Unified Model is being developed, using a nested approach. This model application, referred to as EMEP4UK, has been developed at a 5 × 5 km₂ resolution covering the whole of the British Isles. By comparison with existing statistical models of atmospheric chemistry and transport over the UK (e.g. Singles et al. 1998; Lee et al. 2000; Metcalfe et al. 2001; Fournier et al. 2005; Vieno 2006; Dore et al. 2007), the EMEP4UK model therefore has the advantage of using real time meteorology, enabling the interactions between emissions, meteorology, concentrations and deposition to be addressed at a fine spatial scale.