Deposition and emissions of reactive nitrogen over European forests: A modelling study

The EMEP MSC-W Eulerian chemical transport model is used to investigate a number of features concerning the concentrations and depositions of reactive nitrogen species over Europe, with a focus on forest ecosystems and soil emissions. We illustrate the relative contributions of oxidised versus reduced nitrogen, and of dry versus wet deposition, to nitrogen inputs to forests. A comparison with measurements, including data for the NOFRETETE sites, showed that the EMEP model performs generally well for N-compounds, although with some problems for NH3 which is difficult to model with a large-scale model. The model was modified to make use of a new forest-soil–NO inventory (with daily resolution) from the NOFRETETE project and used to calculate the potential effects of these emissions on N-deposition to forests, and on the ozone-indicator AOT40. The contribution of soil–NO to these environmental measures was found to be generally small, but significant in some areas, with changes ranging between 0–20% in Central Europe and even greater in Scandinavia. Given the large uncertainties in soil–NO emission estimates, it is clear that this source is potentially comparable in its importance to many combustion sources in parts of Europe, and deserves more attention.