Deposition of Sulfur and Nitrogen in the Nordic Countries: Present and Future

The deposition of sulfur and inorganic nitrogen on an ecosystem level over the Nordic countries was estimated using monitoring results on wet deposition, throughfall and air concentrations and literature data on nitrogen deposition velocities. The aim of the work was to obtain deposition data relevant for comparison with critical loads for forest soils and for producing maps to show where critical loads were exceeded in forest ecosystems. Wet deposition data, from relatively dense networks over all the Nordic countries, formed the basis of the mapping procedure. Dry deposition, calculated for nitrogen from air pollution concentrations and deposition velocities and for sulfur from air concentrations and specific deposition factors derived from throughfall measurements, was added to the wet deposition data. The link between deposition at the ecosystem level and large-scale air pollution movements over Europe is not fully understood. This has to be considered when using the levels at which critical loads are exceeded as a basis for abatement strategy calculations for reducing acid deposition over Europe.