In this study an alternative has been taken, by applying an atmospheric transport model. Due to assumptions in the treatment of vertical dispersion, many current UK models are unable to describe the short-range dispersion of ammonia adequately, so a new statistical model has been created by extensively modifying an existing Lagrangian trajectory model. A number of atmospheric processes have been parameterised for inclusion in the model, and boundary data have been constructed to allow the inclusion of continental emissions. The wind speed data used to advect the model have been optimised for NH<SUB>3</SUB> dry deposition, and careful restructuring of the computer code has reduced computational time considerably. Initial testing of the model on a 20 km x 20 km grid has shown that modelled wet deposition fluxes of sulphate and nitrate have a fair degree of success in reproducing measurement data. Comparisons of SO<SUB>2</SUB> and NO<SUB>2</SUB> surface concentrations with measured data have shown a variable degree of success, highlighting the uncertainties in emission heights. A number of sensitivity tests have been performed on various models processes, and have shown the degree of dependence of certain modelled species on the type of parameterisation used in the model. Emissions data for NH<SUB>3</SUB> have been employed on a much finer horizontal scale of 5 km x 5 km grid squares than has been previously used in an atmospheric transport model over Great Britain. The use of a detailed description of vertical diffusion and dry deposition, together with a fine resolution emissions dataset, have produced the best yet agreement with measured NH<SUB>3</SUB> surface concentration estimates for Great Britain. Total annual fluxes of NH<SUB>3</SUB> dry deposition agree well with official estimates, but the spatial distribution of these data differ considerably, and highlight the possible over-estimation of the NH<SUB>3</SUB> samplers used in the monitoring network in areas of very low surface concentrations. A total annual budget for reduced nitrogen is given which shows the directional-dependence of both total deposition and export of reduced nitrogen. The model estimates that on average over half of the total dry deposition is the result of emissions being dry deposited in the same 5 km grid square. The spatial variation of this fraction is important information which can be used to guide emission reduction strategies.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:661987 |
| Date | January 1996 |
| Creators | Singles, Roderick John |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14431 |
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