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Indicator Assessment
Exposure of ecosystems to acidification
Note: The maps show the average accumulated exceedance of critical loads for acidification in 1980 (top left), 1990 (top right), 2000 (middle left), 2010 (middle right), 2020 under the revised Gothenburg Protocol scenario emission reduction agreements (bottom left) and 2030 assuming maximum technically feasible reduction (bottom right).
Exposure of ecosystems to eutrophication
Note: The maps show areas where critical loads for eutrophication of freshwater and terrestrial habitats are exceeded (CSI 005) by nitrogen depositions caused by emissions between 1980 (top left) and 2030 (bottom right)
Rural concentration of the ozone indicator AOT40 for crops
Note: Accumulated ozone exposure values, over a threshold of 40 parts per billion, for crops (AOT40c) increase from northern Europe towards the southern Mediterranean countries.
Rural concentration of the ozone indicator AOT40 for forest
Note: The gradient of the accumulated ozone exposure values over a threshold of 40 parts per billion for forests (AOT40f) is similar to that of the AOT40c (crops). AOT40f increases from northern Europe to reach the highest values in the countries around the Mediterranean.
Acidification and eutrophication
Exceedances of critical loads for acidification
An assessment made by applying the same scientific methods used at the time policy objectives were set, shows that the 2010 interim objective for acidification set in the National Emission Ceiling Directive 2001/81/EC (NEC Directive) was achieved in the vast majority of grid cells across the EU. This means that the area at risk was reduced by more than 50% in comparison to 1990 in all Member States, except for one grid cell located in northern Germany (EEA, 2012; Hettelingh et al., 2013).
Figure 1 shows the exposure and area at risk for European countries between 1980 and 2030, using updated scientific knowledge developed since 2000 (see “policy context” in the Indicator Specification). The reduction of anthropogenic acidifying emissions since 1980 (see CSI040) is evident. For example, the areas shaded red on the maps (exceedances of more than 1 200 equivalents per hectare per year (eq ha–1a–1)) show a clear reduction between 1980 and 2010. In the EU-28, the ecosystem area where acidification critical loads were exceeded decreased from peak values of 43% in 1980 to 7% in 2010 (7% across all EEA member countries). However, in 2010, several areas in the EU-28 did not meet the National Emission Ceiling Directive's (2001/81/EC) interim objective for acidification. When implementing current legislation, only 4% of the EU-28 ecosystem area is projected to be in exceedance in 2020 (3% in EEA member countries; see CCE 2014). A few hot spots can still be found particularly in the Czech Republic, the Netherlands and Poland. When considering uncertainties in the calculations, the projected area at risk in 2030 is not significantly further reduced if a 'maximum technically feasible reduction' (MTFR) scenario is assumed.
Exceedances of critical loads for eutrophication
When considering the European Union (EU) area as a whole, an assessment performed on the basis of 2000 knowledge indicated that the area at risk of eutrophication was reduced by 34% in the EU-27 as a whole, thus meeting the NEC Directive's objective at EU level (EEA, 2012).
However, this is only the case when the original average nitrogen deposition modelling approach is employed to assess attainment. Figure 2 shows the development of eutrophication critical load exceedances in Europe starting in 1980, if present scientific knowledge is applied (see “policy context” in the Indicator Specification). It also shows the projection of the exceedances in 2020 (current legislation scenario), and the projection of exceedances in 2030 according to a MTFR scenario. The EU-28 ecosystem area, where the critical loads for eutrophication were exceeded, peaked at 84% in 1990 and decreased to 63% in 2010 (55% in EEA member countries). Most central European areas with very high exceedances in 1980 (red shading: larger than 1200 equivalents of nitrogen per hectare per year), are on track to be markedly reduced by 2020. However, modelling results predict that there will still be hot spots with very high exceedances in western France and the border areas between Belgium, Germany and the Netherlands as well as in northern Italy.
According to the scenario analyses, the European area at risk due to atmospheric nutrient nitrogen deposition will decrease in the EU-28 from 63% in 2010 to 54% in 2020 under the amended Gothenburg Protocol (55% and 48%, respectively, in EEA member countries). Thus, in 2020, more than 50% of the ecosystem areas classified according to EUNIS are still expected to be at risk of excessive atmospheric nitrogen (N) deposition in the EU. However, the magnitude of exceedance is predicted to reduce considerably in those areas (see the equivalent N per hectare and year ranges in Figure 2). In the EU-28, the area at risk of eutrophication is projected to decrease only slightly by 2030. The updated air pollution strategy proposed by the European Commission in late 2013 aims to achieve a situation where the EU-28 ecosystem area exceeding critical loads for eutrophication is reduced by 35% by 2030, relative to 2005. This target would be met in 2030 under an MTFR scenario, but would not be met if only current legislation were fully implemented.
Ground-level ozone pollution
The target value threshold for the protection of vegetation is exceeded in a substantial fraction of the agricultural area in the EEA33 member countries (excluding Turkey, see note in Figure 3). In 2012, this is the case in about 27% of a total area of 2.063 million km2 (Figures 3 and 4). Exceedances of the target value threshold have been observed in southern and eastern Europe (see red and violet areas in Figure 5). The long-term objective is met in 14% of the total agricultural area (green areas in figure 5), mainly in Estonia, Finland, Iceland, Ireland, Norway, Sweden and the United Kingdom.
In 2003, the meteorological conditions were very favorable for ozone formation resulting in exceptionally high concentrations. Also in June and July 2006 there were a large number of ozone episodes (EEA, 2007), resulting in much higher accumulated ozone exposure value over a threshold of 40 parts per billion (AOT40) compared to other years.
Based on a model calculation, the NEC Directive 2010 interim objective for critical levels was met in the EU, except in parts of Spain and Portugal. The interim objective for the ozone accumulated concentration is clearly not achieved in most of Europe. An evaluation of the two objectives on the basis of actual measurements is difficult, due to the lack of monitoring stations in the early 1990s. However, the limited number of available observed time series suggests a rather less optimistic situation than do the model calculations (EEA, 2012).
Figure 6 shows AOT40 results for forests (AOT40f). The gradients of the AOT40f values are similar to those of the AOT40 for crops/protection of vegetation: relatively low in northern Europe with the highest values observed in the countries around the Mediterranean. The critical level is met (green areas) in Finland, Iceland, Ireland, and the United Kingdom, and parts of Denmark, Estonia, Norway and Sweden, and the Atlantic coasts in northwest Europe (the total forested area with concentrations below the critical level is 37% of a total area of 1.44 million km2). In southern Europe, levels may be as high as 4-5 times above the critical level (red and violet areas in Figure 6).
Figure 7 summarises the exposure of forested areas between 2004 and 2012, when large variations were observed. While in 2004 and 2006, almost all forests were exposed to levels exceeding the critical level, in 2007 40% was exposed to levels lower than the critical level. This percentage has been more or less stable since then (with a decrease in 2008). Similarly to the AOT40 for crops/protection of vegetation, no significant upward or downward trend could be detected.
Acidification and eutrophication
In most European countries, the area at risk of acidification was below 10% in 2010 and is projected to decrease further by 2020, when current legislation is fully implemented (Figure 8). In addition, the magnitude of exceedance was below 50 eq H+ ha-1 a-1 in most countries in 2010, and will reach values close to zero in 2020. However, there are a few exceptions, particularly in the Czech Republic, Lithuania, the Netherlands and Poland where exceedances were still high in 2010 and the acidification problem is not predicted to be solved by 2020.
As SO2 emissions have fallen, the relative contribution made by ammonia (NH3) emitted from agricultural activities and nitrogen oxides (NOX) emitted from combustion processes to surface water and soil acidification has increased or become predominant in some regions in Europe.
The ecosystem area where critical loads for nutrient nitrogen are exceeded was still close to 100% in many European countries in 2010 (Figure 9). Although a decrease is predicted by 2020 if current legislation is implemented, the area showing exceedances will be above 50% in most countries. Extremely high magnitudes of exceedances can be found in countries exposed to high nitrogen deposition, both in 2010 and 2020, particularly in the Netherlands, Luxembourg, Denmark, Hungary and Switzerland. This is due to high nitrogen deposition rates and/or ecosystems, such as nutrient poor grasslands, which are very sensitive to an excess supply of nitrogen via the atmosphere (see for example EEA, 2014c).
Ozone
Observed AOT40 concentrations for crops indicate increasing ecosystem exposure, but with large variations. Between 1996 and 2012, there were 256 rural background stations providing valid data during at least 13 of the 17 years (Figure 10). At 36 (14%) of the stations, the time series have a tendency to increase, although this increase is not statistically significant at any of the stations. Of the other 220 stations where a downward tendency was observed, 47 show a significant downward trend.
This indicator shows the negative impact of air pollution on ecosystems and vegetation in Europe. In particular, it shows:
In the case of acidification and eutrophication, the area as well as the magnitude of critical load exceedances in ecosystems are shown. A critical load is a quantitative estimate of an exposure to one or more pollutants, below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge (ICP on Modelling and Mapping, 2015; UNECE, 2015). It represents the upper limit of one or more pollutants deposited on the Earth's surface that an ecosystem, such as a lake or a forest, can tolerate without its function (e.g. the nutrient nitrogen cycle) or its structure (e.g. with respect to plant species' richness) being damaged.
A positive difference between the deposition loads of acidifying and/or eutrophying airborne pollutants and the critical loads is termed an 'exceedance'.
In the case of ozone, the risk is estimated by reference to the 'critical level' for ozone for each location. This is a concentration of ozone in the atmosphere, above which direct adverse effects on receptors, such as human beings, plants, ecosystems or materials, may occur according to present knowledge (ICP on Modelling and Mapping, 2015; UNECE, 2015).
Acidification and eutrophication
Ozone
Ozone concentrations: micrograms of ozone per cubic meter (µg/m³) or parts per billion (ppb). 1 ppb ~ 2 µg/m³.
AOT40estimate = AOT40measured x [(total possible number of hours )/(number of measured hourly values)]
Where “total possible number of hours” is the number of hours within the time period of AOT40 definition, (i.e. 08:00 to 20:00 h CET from 1 May to 31 July each year, for vegetation protection and from 1 April to 30 September each year for forest protection)
This indicator provides relevant information for the EU's Seventh Environmental Action Programme (7th EAP) and the new Clean Air Programme for Europe proposed by the European Commission at the end of 2013. The long-term strategic objective and core of the new air package is to attain 'air quality levels that do not give rise to significant negative impacts on, or risks for, human health and the environment'. The 7th EAP kept the intermediate objectives already set in the 6th EAP and the 2005 Thematic Strategy on Air Pollution to further reduce air pollution and its impacts on ecosystems and biodiversity by 2020. This will be accomplished by achieving full compliance with existing legislation. Furthermore, the long-term objective to not exceed critical loads and levels remains in place.
Internationally, a first step to address air-pollution related impacts on health and the environment was the 1979 United Nations Economic Commission for Europe (UNECE) Geneva Convention on Long-range Transboundary Air Pollution (LRTAP Convention).
A centrepiece of the convention is the 1999 Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-level Ozone, subsequently amended in 2012. This protocol set national ceilings (limits) for the main air pollutants and established the critical loads concept as a tool to inform political discussions concerning damage to sensitive ecosystems. Critical ozone levels for vegetation were also defined under the LRTAP Convention.
The Gothenburg Protocol was followed in 2001 by the EU's National Emission Ceilings (NEC) Directive (EU, 2001), which set specific environmental objectives addressing acidification and eutrophication impacts on ecosystems, to be met by 2010. The directive introduced legally binding national emissions limits for four main air pollutants, including three important pollutants that contribute to acidification and eutrophication: sulphur dioxide (SO2), nitrogen oxides (NOX) and ammonia (NH3). Furthermore, the directive defines national emissions ceilings for ozone precursors, non-methane volatile organic compounds and NOx. The directive requires EU Member States to have met emissions ceilings by 2010 and in subsequent years, although in reality around half of all Member States had missed at least one of their ceilings by 2010 (EEA, 2014b). A revision of the NEC Directive is part of the Clean Air Programme for Europe proposed by the European Commission at the end of 2013. It aims at compliance with the amended Gothenburg Protocol by 2020, followed by more ambitious reductions from 2030 onwards.
The Air Quality Directive (EU, 2008) sets both a target value (to be met in 2010) and a long-term objective for ozone for the protection of vegetation. The long-term objective is largely consistent with the long-term critical level of ozone for crops (UNECE, 2015), as defined in the UNECE LRTAP Convention.
When performing an assessment of progress made in reducing harm caused by air pollution, advances in scientific knowledge since the approval of the NEC Directive should clearly not be disregarded. These allow a more accurate picture to be obtained than by using the original techniques alone. Such developments include the facts that:
The NECD (EU, 2001) sets pollutant-specific and legally binding emissions ceilings for nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOC), sulphur dioxide (SO2) and ammonia (NH3) for each EU Member State. The directive sets specific environmental objectives that address acidification and eutrophication impacts on ecosystems and the harmful effects of ozone on vegetation and human health. The directive requires the Member States to have met the ceilings and interim environmental objectives by 2010 and in subsequent years.
The NEC Directive's 2010 interim objective for the protection of sensitive ecosystems from acidification aims to reduce areas where critical loads of acid deposition are exceeded by at least 50 % (in each grid cell) compared with the 1990 situation. The eutrophication objective under the NEC Directive aims to reduce areas with depositions of nutrient nitrogen in excess of the critical loads by about 30 % in 2010 compared with 1990.
The interim environmental objective for vegetation-related ground-level ozone exposure is to reduce the ground-level ozone load above the critical level for crops and semi-natural vegetation (AOT40 = 3 ppm/hour) by one-third in all grid cells by 2010, compared with the 1990 situation. In addition, the ground-level ozone accumulated concentration shall not exceed an absolute limit of 10 ppm per hour, expressed as an exceedance of critical accumulated concentration in any grid cell.
Using a stepwise approach and taking into account advances in scientific knowledge, the long-term target under the amended protocol is that atmospheric depositions or concentrations do not exceed:
a) for parties within the geographical scope of the European Monitoring and Evaluation Programme (EMEP) and Canada, the critical loads of acidity, as described in annex I, that allow ecosystem recovery;
b) for parties within the geographical scope of EMEP, the critical loads of nutrient nitrogen, as described in annex I, that allow ecosystem recovery; and
c) for parties within the geographical scope of EMEP, the critical levels of ozone, as given in annex I.
Annex I of the amended protocol includes a short definition of critical loads for acidification/eutrophication and critical levels for ozone.
Critical levels for the protection of crops and forests (AOT40f) have also been defined under the LRTAP Convention (UNECE, 2015). The critical level for crops is consistent with the EU long-term objective for vegetation. The critical level for forests relates to the accumulated sum during the growing season (considered as April to September) and is set to 10 000 μg/m3·h.
For the protection of vegetation from ozone exposure, the Air Quality Directive (EU, 2008) defines:
a) the target value for the protection of vegetation as AOT40-value (calculated from hourly values from May to July, considering the growing season) of 18 000 (μg/m3)·h, averaged over five years. This target value should be met in 2010 (2010 being the first year from which data will be used in the calculation over the following five years).
b) a long-term objective as AOT40-value (calculated from hourly values from May to July) of 6 000 (μg/m3)·h, with no defined date of attainment.
In the assessment part of the indicator, the target value threshold is also considered. This is the target value considered only for one year and not for the averaged period of five years.
New air policy objectives for 2030 are specified in the Clean Air Programme for Europe proposed by the European Commission in 2013, in line with the long term objective of reaching no exceedance of the critical loads and levels: in 2030, the ecosystem area exceeding eutrophication limits will be 35 % of the area in 2005.
For the area where critical loads for acidification or eutrophication are exceeded, a percentage of the total ecosystem area in each grid cell can be calculated. 'Total ecosystem area' is defined as the area of ecosystem-types classified according to the EUNIS Habitats classification (EEA, 2014d). The European background information used around 2001, when the NEC Directive was adopted, covered only forest ecosystems (EUNIS class G) and freshwaters. Now semi-natural vegetation (EUNIS classes D, E and F) is also included. For details on changes in the scientific knowledge base since 2001, please see EEA (2012 and 2014c); Hettelinghet al. (2013) and CCE (2014).
An AAE can be computed for an ecosystem, a grid cell and any region or country for which multiple critical loads and deposition values are available.
The European database of critical loads for acidification and eutrophication used in this indicator is compiled by the Coordination Centre for Effects (CCE) under the Convention on Long-range Transboundary Air Pollution. 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 the so-called Mapping Manual (UNECE, 2015), 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 following consensus of Parties to the LRTAP Convention (including most EEA33 member countries).
AOT40 estimated values are calculated from hourly data (EU, 2008) at all rural background stations available in AirBase. Only data series with more than 75 % valid data are considered.
The AOT40 maps have been created by combining measurement data from the rural background stations combined with the results of the EMEP dispersion model (EMEP, 2014), altitude field and surface solar radiation in a linear regression model, followed by the interpolation of its residuals by ordinary Kriging (Horalek et al, 2013). For altitude, dataset GTOPO30 (Global Digital Elevation Model) at a resolution of 30 x 30 arcseconds has been used. The solar radiation has been obtained from ECMWF's Meteorological Archival and Retrieval System (MARS). Kriging is a method of spatial statistics (N. Cressie, 1993) that makes use of spatial autocorrelation (the statistical relationship between the monitoring points expressed in the form of variograms). Kriging weights the surrounding measured values to derive an interpolation for each location. The weights are based (i) on the distance between the measured points and the interpolated point, and (ii) on the overall spatial arrangement among the measured points. The type of Kriging at its parameters (in particular the parameters describing the semivariogram) is chosen in order to minimise the RMS error.
The AOT40 maps have been overlayed in a geographical information system with the land cover CLC2006 map. The resolution was 500 x 500 m2 to generate maps for the agricultural area at risk due to ozone exposure. Exposure of the agricultural area (defined as the land cover level-1 class 2 Agricultural areas encompassing the level-2 classes 2.1 Arable land, 2.2 Permanent crops, 2.3 Pastures and 2.4 Heterogeneous agricultural areas) and forest areas (defined as the land cover level-2 class 3.1. Forests) have been calculated at the country-level.
The temporal trends have been estimated using a Mann-Kendal statistical test. This test is particularly useful since missing values are allowed and the data need not conform to any particular distribution. Moreover, as only the relative magnitudes of the data rather than their actual measured values are used, this test is less sensitive to incomplete data capture and/or special meteorological conditions leading to extreme values (Gilbert, 1987).
AOT40 is used to be in line with the Air Qaulity Directives. However, in considering the latest scientific knowledge concerning vegetation ozone exposure, it should be noted that, at present, ozone impacts on vegetation are better modelled by fluxes of ozone into stomatal openings of vegetation (Mills et al., 2011a and 2011b).
Since the critical loads exceedance approach is a tool used in policy-related analysis, the assessment of biases and robustness of approach is a major focus when addressing uncertainties. This assessment is also determined by the uncertainties in the emissions and atmospheric dispersion modelling estimates, and the scenarios used. Sensitivity analyses using, for example, different emissions estimates for future years or excluding the correlation in the dispersion of pollutants give information on the uncertainty range (Hettelingh et al., 2012).
A comprehensive uncertainty analysis of the integrated assessment approach, including ecosystem effects (critical loads) was compiled by Suutari et al. (2001).
This indicator provides information on the area for which monitoring information is available. In previous years, yearly changes in monitoring density influenced the total monitored area. By using interpolated maps, this problem is largely solved; maps are less sensitive for changes in the central part of the network (though more sensitive for changes in the number of stations in the outskirts).
The indicator is also subject to year-to-year fluctuations as it is mainly sensitive to episodic conditions, and these depend on particular meteorological situations, the occurrence of which varies from year to year. When averaging over Europe, this meteorologically induced variation may be less, provided spatial data coverage is sufficient. Methodology uncertainty is also given by uncertainty in mapping AOT40 based on the interpolation of point measurements at background stations. The mean interpolation uncertainty of the map of AOT40 for crops is estimated to be about 35 %.
National Focal Centres compute critical loads and submit data to the Coordination Centre for Effects (CCE) at regular intervals following the consensus of Parties to the LRTAP Convention (including most EEA-33 member countries). The CCE uses a European background database to compute critical loads for ecosystems in countries that do not submit data.
Five main categories for uncertainties in data inputs have been suggested for the calculation of the critical loads themselves, with category 1 being the least certain (Skeffington, 2006):
Skeffington (2006) concludes in his literature review analysis that “although the values for the input parameters are often poorly known, the resulting critical loads are not so uncertain as to make them unusable for environmental policy development”.
Most data have been officially submitted to the Commission under the Exchange of Information Decision (EU, 1997) and/or to EMEP under the LRTAP Convention. Air quality monitoring station characteristics and representativeness may not be well documented, which may imply that stations that are not representative for background conditions have been included, probably leading to a slight underestimation of the indicator. Coverage of territory and time may be incomplete. The different definition of AOT40-values (accumulation during 08.00 to 20.00 CET following the Air Quality Directive (EU, 2008) versus accumulation during daylight hours following the definition in the NEC Directive (EU, 2001)) is expected to introduce minor inconsistencies in the data sets.
• Ozone
This indicator is rather sensitive to the precision at the reference level (40 ppb or 80 micrograms per m3)
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/exposure-of-ecosystems-to-acidification-3/assessment-1 or scan the QR code.
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