EMEP Eulerian model for atmospheric transport and deposition of nitrogen species over Europe

Abstract As a part of EMEP, MSC-W in Oslo has the task to compute atmospheric transport and deposition of sulphur and nitrogen species over Europe. To perform this task, a three-dimensional Eulerian multilayer model was developed at MSC-W. This model has a 50 km horizontal resolution with 20 vertical layers, of which 10 are below 2 km level. Meteorological input, from a dedicated weather prediction model, is updated at 6-hour intervals. Emission inventories for NO x (NO + NO 2 ), NH 3 (and SO 2 ), submitted officially by the individual countries, are used as input data. In the model, NO x may be converted to PAN by the CH 3 COO 2 radical, or to nitrate (as HNO 3 in the gas phase and ammonium nitrate as particulate matter). The oxidation of NO x is assumed to proceed either by the OH radical in the gas phase, or as a night-time reaction via N 2 O 5 on deliquescent particles. Both OH and CH 3 COO 2 are prescribed as a function of solar zenith angle and cloud cover. Furthermore, ammonium sulphate is formed by NH 3 and sulphate. Excess NH 3 may react with HNO 3 , forming ammonium nitrate in an equilibrium reaction. Nitrogen is removed from the atmosphere by dry and wet deposition. A description of the model, as well as the model results, are presented and discussed. We also present a comparison of calculated concentrations and deposition fields for nitrogen with available measurements of concentrations and wet deposition for 1992.