An overview is given on modeling of the atmospheric transport and deposition of ammonia and ammonium for different purposes on different scales and the problems associated with the validation of such models. The various processes that are part of such models are discussed as well as the problems with obtaining the relevant information. The issue of short vs. long distance transport will be discussed. An example is given of local modeling of ammonia deposition.
(1) E-mail: Willem.Asman@agrsci.dk