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Recent research in nitrogen exchange with the atmosphere has separated research communities according to N form. The integrated perspective needed to quantify the net effect of N on greenhouse-gas balance is being addressed by the NitroEurope Integrated Project (NEU). Recent advances have depended on improved methodologies, while ongoing challenges include gas–aerosol interactions, organic nitrogen and N2 fluxes. The NEU strategy applies a 3-tier Flux Network together with a Manipulation Network of global-change experiments, linked by common protocols to facilitate model application. Substantial progress has been made in modelling N fluxes, especially for N2O, NO and bi-directional NH3 exchange. Landscape analysis represents an emerging challenge to address the spatial interactions between farms, fields, ecosystems, catchments and air dispersion/deposition. European up-scaling of N fluxes is highly uncertain and a key priority is for better data on agricultural practices. Finally, attention is needed to develop N flux verification procedures to assess compliance with international protocols.

Recent research in nitrogen exchange with the atmosphere has separated research communities according to N form. The integrated perspective needed to quantify the net effect of N on greenhouse-gas balance is being addressed by the NitroEurope Integrated Project (NEU). Recent advances have depended on improved methodologies, while ongoing challenges include gas-aerosol interactions, organic nitrogen and N2 fluxes. The NEU strategy applies a 3-tier Flux Network together with a Manipulation Network of global-change experiments, linked by common protocols to facilitate model application. Substantial progress has been made in modelling N fluxes, especially for N2O, NO and bi-directional NH3 exchange. Landscape analysis represents an emerging challenge to address the spatial interactions between farms, fields, ecosystems, catchments and air dispersion/deposition. European up-scaling of N fluxes is highly uncertain and a key priority is for better data on agricultural practices. Finally, attention is needed to develop N flux verification procedures to assess compliance with international protocols.; Current N research is separated by form; the challenge is to link N components, scales and issues.

Recent research in nitrogen exchange with the atmosphere has separated research communities according to N form. The integrated perspective needed to quantify the net effect of N on greenhouse-gas balance is being addressed by the NitroEurope Integrated Project (NEU). Recent advances have depended on improved methodologies, while ongoing challenges include gas-aerosol interactions, organic nitrogen and N2 fluxes. The NEU strategy applies a 3-tier Flux Network together with a Manipulation Network of global-change experiments, linked by common protocols to facilitate model application. Substantial progress has been made in modelling N fluxes, especially for N2O, NO and bi-directional NH3 exchange. Landscape analysis represents an emerging challenge to address the spatial interactions between farms, fields, ecosystems, catchments and air dispersion/deposition. European up-scaling of N fluxes is highly uncertain and a key priority is for better data on agricultural practices. Finally, attention is needed to develop N flux verification procedures to assess compliance with international protocols.; Current N research is separated by form; the challenge is to link N components, scales and issues.

Recent research in nitrogen exchange with the atmosphere has separated research communities according to N form. The integrated perspective needed to quantify the net effect of N on greenhouse-gas balance is being addressed by the NitroEurope Integrated Project (NEU). Recent advances have depended on improved methodologies, while ongoing challenges include gas–aerosol interactions, organic nitrogen and N2 fluxes. The NEU strategy applies a 3-tier Flux Network together with a Manipulation Network of global-change experiments, linked by common protocols to facilitate model application. Substantial progress has been made in modelling N fluxes, especially for N2O, NO and bi-directional NH3 exchange. Landscape analysis represents an emerging challenge to address the spatial interactions between farms, fields, ecosystems, catchments and air dispersion/deposition. European up-scaling of N fluxes is highly uncertain and a key priority is for better data on agricultural practices. Finally, attention is needed to develop N flux verification procedures to assess compliance with international protocols.

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.

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.

Forest soils are a significant source for the primary and secondary greenhouse gases N2O and NO. However, current estimates are still uncertain due to the still limited number of field measurements and the herein observed pronounced variability of N trace gas fluxes in space and time, which are due to the variation of environmental factors such as soil and vegetation properties or meteorological conditions. To overcome these problems we further developed a process-oriented model, the PnET-N-DNDC model, which simulates the N trace gas exchange on the basis of the processes involved in production, consumption and emission of N trace gases. This model was validated against field observations of N trace gas fluxes from 19 sites obtained within the EU project NOFRETETE, and shown to perform well for N2O (r2=0.68, slope=0.76) and NO (r2=0.78, slope=0.73). For the calculation of a European-wide emission inventory we linked the model to a detailed, regionally and temporally resolved database, comprising climatic properties (daily resolution), and soil parameters, and information on forest areas and types for the years 1990, 1995 and 2000. Our calculations show that N trace gas fluxes from forest soils may vary substantial from year to year and that distinct regional patterns can be observed. Our central estimate of NO emissions from forest soils in the EU amounts to 98.4, 84.9 and 99.2 kt N yr−1, using meteorology from 1990, 1995 and year 2000, respectively. This is <1.0% of pyrogenic NOx emissions. For N2O emissions the central estimates were 86.8, 77.6 and 81.6 kt N yr−1, respectively, which is approx. 14.5% of the source strength coming from agricultural soils. An extensive sensitivity analysis was conducted which showed a range in emissions from 44.4 to 254.0 kt N yr−1 for NO and 50.7 to 96.9 kt N yr−1 for N2O, for year 2000 meteorology. The results show that process-oriented models coupled to a GIS are useful tools for the calculation of regional, national, or global i

Forest soils are a significant source for the primary and secondary greenhouse gases N2O and NO. However, current estimates are still uncertain due to the still limited number of field measurements and the herein observed pronounced variability of N trace gas fluxes in space and time, which are due to the variation of environmental factors such as soil and vegetation properties or meteorological conditions. To overcome these problems we further developed a process-oriented model, the PnET-N-DNDC model, which simulates the N trace gas exchange on the basis of the processes involved in production, consumption and emission of N trace gases. This model was validated against field observations of N trace gas fluxes from 19 sites obtained within the EU project NOFRETETE, and shown to perform well for N2O (r2=0.68, slope=0.76) and NO (r2=0.78, slope=0.73). For the calculation of a European-wide emission inventory we linked the model to a detailed, regionally and temporally resolved database, comprising climatic properties (daily resolution), and soil parameters, and information on forest areas and types for the years 1990, 1995 and 2000. Our calculations show that N trace gas fluxes from forest soils may vary substantial from year to year and that distinct regional patterns can be observed. Our central estimate of NO emissions from forest soils in the EU amounts to 98.4, 84.9 and 99.2 kt N yr−1, using meteorology from 1990, 1995 and year 2000, respectively. This is <1.0% of pyrogenic NOx emissions. For N2O emissions the central estimates were 86.8, 77.6 and 81.6 kt N yr−1, respectively, which is approx. 14.5% of the source strength coming from agricultural soils. An extensive sensitivity analysis was conducted which showed a range in emissions from 44.4 to 254.0 kt N yr−1 for NO and 50.7 to 96.9 kt N yr−1 for N2O, for year 2000 meteorology. The results show that process-oriented models coupled to a GIS are useful tools for the calculation of regional, national, or global i