Modelling deposition and air concentration of reduced nitrogen in Poland and sensitivity to variability in annual meteorology

The relative contribution of reduced nitrogen to acid and eutrophic deposition in Europe has increased recently as a result of European policies which have been successful in reducing SO2 and NOx emissions but have had smaller impacts on ammonia (NH3) emissions. In this paper the Fine Resolution Atmospheric Multi pollutant Exchange (FRAME) model was used to calculate the spatial patterns of annual average ammonia and ammonium (NH4) air concentrations and reduced nitrogen (NHx) dry and wet deposition with a 5km x 5km grid for years 2002–2005. The modelled air concentrations of NH3 and dry deposition of NHx show similar spatial patterns for all years considered. The largest year to year changes were found for wet deposition, which vary considerably with precipitation amount. The FRAME modelled air concentrations and wet deposition are in reasonable agreement with available measurements (Pearson’s correlation coefficients above 0.6 for years 2002–2005), and with spatial patterns of concentrations and deposition of NHx reported with the EMEP results, but show larger spatial gradients. The error statistics show that the FRAME model results are in better agreement with measurements if compared 33 with EMEP estimates. The differences in deposition budgets calculated with FRAME and EMEP do not exceed 17% for wet and 6% for dry deposition, with FRAME estimates higher than for EMEP wet deposition for modelled period and lower or equal for dry deposition. The FRAME estimates of wet deposition budget are lower than the measurement-based values reported by the Chief Inspectorate of Environmental Protection of Poland, with the differences by approximately 3%. Up to 93% of dry and 53% of wet deposition of NHx in Poland originates from national sources. Over the western part of Poland and mountainous areas in the south, transboundary transport can contribute over 80% of total (dry+wet) NHx deposition. The spatial pattern of the relative contribution of national sources to total deposition of NHx may change significantly due to the general circulation of air.