Modelling the atmospheric transport and deposition of ammonia and ammonium: an overview with special reference to Denmark

Requirements for NHx models are discussed. It is very important that such m odels can describe the dry deposition of NH3 close to sources well. A descr iption is given of all processes that should be included as well as referen ces to relevant literature. For the calculation of long-term average deposi tions, some of these processes must be parameterized in order to keep the c pu time within reasonable bounds. Which processes should be parameterized d epends on the purpose of the model calculations. A Langrangian plume model using a Gaussian plume description or a K-model with many layers can be use d to model NHx deposition to nature areas embedded in agricultural areas in northern Europe (spatial resolution <5 x 5 km(2)). On the other hand long- range transport of NHx can be modelled with Lagrangian or Eulerian models w ith correction factors to calculate dry deposition of NH3 close to the sour ce correctly (spatial resolution of 1-layer models > 50 x 50 km(2)). TREND, a statistical atmospheric transport model was applied to calculate the con centrations and depositions of NH3 and its reaction product NH4+ aerosol to Denmark and surrounding sea areas on a 5 x 5 km(2) grid. The model is able to reproduce measured NH3 and NH4+ aerosol concentrations reasonably well, as well as NHx wet deposition. It was found that dry deposition constitute s about 66% to the NHx total deposition to the land area of Denmark. Wet de position, however, is relatively more important at sea and constitutes 64-6 7% of the NHx total deposition to the Kattegat and Southern Belt sea areas. (C) 2001 Elsevier Science Ltd. All rights reserved.