Modelling of the Atmospheric Transport and Deposition of Ammonia at a National and Regional Scale

An overview of the current status of the modeling of the atmospheric transport and deposition of ammonia at a national and regional scale is presented. Firstly, the paper deals with the parameterizations of the transport and removal processes of ammonia used in modeling. Subsequently, an overview of the models currently in use describing the ammonia concentration and deposition at a national or (sub-) European scale is given. The emphasis lies on (a) the process parameterizations that are particularly important for ammonia such as the emission, deposition and chemical conversion and (b) the validation with measurements. Finally, discussion items as input to the Working Group 4 session are defined that follow from the model overview and validation. Measurements of ammonia and ammonium concentrations and deposition from monitoring programmes are crucial for providing information about trends and actual loads of ammonia in the environment. Such data may together with data from field campaigns form the basis of our understanding of the physical and chemical processes governing the fate of ammonia. However, modelling of the concentrations and deposition of ammonia extends our possibilities substantially. Measurements are usually carried out at a limited number of locations. Model calculations are therefore used to obtain information with higher geographical resolutions and for estimates of loads at locations not covered by the monitoring network. Well-tested and validated models are furthermore highly useful in the interpretation of the measurements.