Modelling the deposition of reduced nitrogen at different scales in the United Kingdom

Abstract

A national scale atmospheric transport model (FRAME) was applied to the UK to generate maps of ammonia concentration and the wet and dry deposition of reduced nitrogen. The model was found to give satisfactory agreement with measurements from the national monitoring networks of ammonia and ammonium aerosol concentrations and wet deposition of ammonium. Scatter in the model correlation with measurements of ammonia concentration was observed due to the strong sub-model grid (5 km) variation in ammonia concentration. Application of a local dispersion model to calculate ammonia concentrations emitted from a typical poultry unit showed that areas of high concentration were restricted to a 1 km2 area surrounding the point source. FRAME showed good overall agreement with the EMEP model for national average levels of ammonia concentration and reduced nitrogen deposition. However, a difference in spatial patterns of wet deposition occurred due to the different treatment of precipitation in the two models. It was concluded that finer resolution national scale modelling of reduced nitrogen is required in order to improve estimates of critical loads exceedance for acid deposition and nutrient nitrogen deposition.