This indicator investigates the exceedance of the critical loads for atmospheric nitrogen deposition in the EEA member and cooperating countries.
Areas where critical loads for eutrophication are exceeded are given as percentages of the total ecosystem area in each grid cell. ‘Total ecosystem area’ is defined as the area of ecosystem types classified according to the European Nature Information System (EUNIS) habitats classification. European background information from around 2001, when the National Emission Ceilings Directive (2001/81/EC) was adopted, covered only forest ecosystems (EUNIS class G) and freshwater ecosystems. Now, semi-natural vegetation ecosystems (EUNIS classes D, E and F) are also included. For details on changes in the scientific knowledge base since 2001, please see Hettelingh et al. (2017).
The AAE can be computed for an ecosystem, a grid cell or any region or country for which multiple critical loads and deposition values are available.
The European database of critical loads for eutrophication used in this indicator is compiled by the Coordination Centre for Effects (CCE) under the Air Convention. The CCE applies methods that are described in detail in CCE status reports, and adopted by the Task Force of the International Cooperative Programme on Modelling and Mapping (ICP M&M) in a mapping manual, for use by national focal centres (NFCs) under the ICP M&M. NFCs compute critical loads and submit data to the CCE at regular intervals after a consensus has been reached by Parties to the Air Convention (including most EEA member countries).
The CCE uses a European background database to compute critical loads for ecosystems in countries that do not submit data.
Input sources for critical load calculations include:
· nitrogen dose-response relationships, provided/updated under the Air Convention’s Working Group on Effects, based on latest scientific knowledge
· ecosystem types defined according to the EUNIS habitats classification (member countries report to the EEA)
· country-specific critical loads of nitrogen for ecosystem types such as nutrient-poor grasslands, forests or freshwater ecosystems (reported by European countries to the CCE)
· for countries that do not submit national data, values from the European background database, maintained by the CCE in collaboration with Wageningen Environmental Research (Alterra)
· gap-filled air pollutant emissions data based on data officially reported under the Gothenburg Protocol (gridded), derived by the Centre on Emission Inventories and Projections (CEIP) at UBA Vienna, Austria
· the European Monitoring and Evaluation Programme (EMEP) atmospheric dispersion model, which simulates how pollutants emitted to the air disperse in the ambient atmosphere (EMEP MSC-West at the Norwegian Meteorological Institute)
· a meteorological driver as an input to the EMEP model (provided by the European Centre for Medium-Range Weather Forecasts (ECMWF))
· modelled ecosystem-specific (gridded) nitrogen deposition rates (nitrate-N plus ammonium-N) for calculating critical load exceedances for single years (EMEP MSC-West at the Norwegian Meteorological Institute)
· monitoring of wet and dry nitrogen deposition, used to calibrate the EMEP model (e.g. monitored by the International Cooperative Programme on Integrated Monitoring, under the Air Convention).
Hindcast (2005) and forecast (2030) emission scenarios, based on the second clean air outlook, were prepared by the International Institute for Applied Systems Analysis (IASA), consultant to the Directorate-General for Environment and the Centre for Integrated Assessment Modelling under the Air Convention.
Target 3 of the European Commission’s zero pollution action plan is for the EU to achieve a reduction of 25% in the ecosystem area where nitrogen deposition is above critical loads for eutrophication by 2030, compared with 2005. The basis for achieving this target is the 2016 National Emission Reduction Commitments Directive (NEC Directive).
The NAPCPs (under Article 6 of the NEC Directive) are the main governance instruments of the NEC Directive and set out how EU Member States must ensure that their emission reduction commitments for 2020-2029 and 2030 onwards are met. With respect to nitrogen, the NEC Directive includes binding commitments for NOx and NH3 emissions.
Target 3 of the zero pollution action plan is realistically expected to be achieved through:
1. the implementation of measures already announced by Member States in their first NAPCPs (see the second clean air outlook and underpinning study) and of further measures to reach the NEC Directive ammonia emission reduction commitments.
2. the implementation of additional measures needed to achieve the 50% reduction in nutrient losses set out in the farm to fork strategy and the nature restoration targets set out in the biodiversity strategy for 2030.
The indicator is also relevant for the ongoing review (2019-2022) and planned revision of the Gothenburg Protocol of the United Nations Economic Commission for Europe’s Convention on Long-Range Transboundary Air Pollution (Air Convention).
Since the critical loads exceedance approach is a tool used in policy-related analysis, assessment of biases and the robustness of the approach are a major focus when addressing uncertainties. This assessment is also affected by the degrees of uncertainty in the emissions and atmospheric dispersion modelling estimates, and the scenarios used. Sensitivity analyses using, for example, different emission estimates for future years or excluding the correlation in the dispersion of pollutants give information on the uncertainty range.
A comprehensive uncertainty analysis of the integrated assessment approach, including ecosystem effects (critical loads), was compiled by Suutari et al. (2001).
The critical loads concept has been applied to the air pollution policy context for several decades (Air Convention and EU legislation).
Critical loads exceedance modelling requires input from many different sources, all of which are well documented and based on international standards/consensus (please see input sources listed under data sources and providers).
For deriving the indicator, the latest scientific knowledge and modelling approaches, consistent with the ones used under the Air Convention (Gothenburg Protocol), are used by the CCE.
Both critical loads and land cover-specific EMEP deposition data are geo-referenced with a harmonised land cover data set, allowing for spatially consistent critical load exceedance maps.