Modelling the spatial distribution of agricultural ammonia emissions in the UK

Accurate models of the spatial distribution of ammonia (NH3) emissions are an essential input to models of atmospheric transport and deposition. This is especially important when resulting deposition maps are used to calculat e patterns of critical loads exceedance or to determine suitable abatement measures. A new methodology has been developed to model the distribution of agricultural ammonia emissions and is applied here for the UK. The model e mploys a specific spatial weighted redistribution of NH3 emission sources o nto suitable landcover types at a 1-km grid level. Key input data to the mo del are agricultural census data, a satellite-based landcover map and estim ates of NH3 emission source strength. The model provides more realistic spa tial NH3 emission estimates than previous models, especially for semi-natur al/natural areas by relocating emission sources from extensively used uplan d areas to the more intensively farmed lowland areas within each parish. At present the model results are summarised as maps at a 5-km grid resolution to reduce uncertainty in the spatial location of NH3 sources. Compared wit h coarser resolution estimates this also provides a more accurate link to c ritical load exceedances. The more accurate redistribution also reduces the apparent critical loads exceedance on upland areas. Results are presented and compared for 1988 and 1996. These show broadly similar patterns between the years, although substantial local changes have occurred, particularly for intensive livestock farming. The model has been used to generate initia l spatially resolved abatement scenarios and provides a general tool for lo cating NH3 emissions that could be applied to other regions.