A computer model has been developed which predicts the concentration and deposition rate of ammonia over Great Britain. Parallelising should reduce run times considerably and allow more realisitic processes to be incorporated.
Ammonia is introduced into the air columns at the surface from a detailed UK emission inventory.
Sulphur dioxide and nitrogen oxides are introduced at various heights from both UK and European source inventories. Vertical diffusion is treated explicitly, with 33 layers of differing depths and with transfer between layers determined by turbulent exchange coefficients. As the air columns move along their trajectories, chemical interactions between ammonia, sulphur dioxide and nitrogen oxides take place and deposition of chemical species occurs at the surface at rates dependent on land use. Wet deposition occurs at rates determined by concentrations, washout coefficients and rainfall rates. Annual mean concentration maps and deposition maps are determined by combining 24 equally-spaced wind directions, suitably weighted by the frequency of winds from each direction.