Air pollution and ecosystems

Figure 9. Summary analysis: air pollution and ecosystems

Introduction

Airborne pollutants are transported in the atmosphere. When these pollutants are deposited on land or water, they can harm ecosystems and habitats. For example, the global mercury cycle results in the ongoing long-range transport of mercury; this negatively affects both terrestrial and marine species (EEA, 2018a).

Key pollutants that potentially harm ecosystems include nitrogen, ground-level ozone, sulphur dioxide (SO₂) and heavy metals. These pollutants are controlled through EU actions under a range of different mechanisms, including the EU’s National Emission Reduction Commitments (NEC) Directive and Air Quality Directive, and the EU’s commitments and related legislative measures aimed at supporting the United Nation’s Convention on Long Range Transboundary Air Pollution. Information on EU emissions of these pollutants is available through the EEA’s air pollutant emissions data viewer (EEA, 2021a).  

Trends in nitrogen and sulphur deposition and their impacts

Eutrophication

The atmospheric deposition of nitrogen in terrestrial ecosystems can result in harmful eutrophication effects in terrestrial, freshwater and marine habitats. This happens when so-called critical loads are exceeded; that is, when the amount of nitrogen deposited exceeds a threshold above which significant impacts may occur. Excess amounts of nitrogen disrupt terrestrial and aquatic ecosystems and lead to changes in species diversity.  

One of the key pollutants closely associated with the exceedance of critical loads is ammonia (NH₃), primarily released from the agricultural sector, which is responsible for 94% of the EU’s NH₃ emissions. From 2005 to 2020, EU-27 emissions of NH₃ fell by only 8% (Figure 10) while reductions in emissions of all other pollutants were much more significant, as explained in the zero pollution cross-cutting story on the National Emissions reduction Commitments Directive (NEC). The main economic activity contributing to emissions of nitrogen oxides (NO_X) (the second main pollutant contributing to eutrophication) is transport (accounting for 43% of emissions in 2020).

Figure 10. Trends in emissions of NH₃, NO_X and SO₂ in the EU-27, 2005-2020 (indexed to 2005) 

Notes: NH₃ = ammonia. NO_x = nitrogen oxides. SO₂ = sulphur dioxide.

Source: EEA (2021).  

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In 2005, nitrogen deposition in the EU-27 exceeded the critical loads for eutrophication in an ecosystem area of 1,235,900km², i.e. 85.5% of the total EU-27 ecosystem area. Between 2005 and 2020, this area decreased by only 12%, as shown in Map 6. The zero pollution action plan target is to achieve a reduction of 25% by 2030 compared with 2005. Based on the current rate of improvement, the EU will not meet the target. The Third Clean Air Outlook (EC, 2022a) also suggests that the target will not be met without further measures and estimates a reduction of only 20% by 2030.

Map 6. Exceedance of atmospheric nitrogen deposition above critical loads for eutrophication in Europe, 2020

Notes: The map shows the ecosystem areas at risk of eutrophication in 2020. Critical loads refer to the upper limits of one or more pollutants deposited on the Earth’s surface that an ecosystem, such as nutrient-poor grasslands or forests, can tolerate without its function (e.g. the nutrient nitrogen cycle) or its structure (e.g. plant species’ richness) being damaged. If the deposition of airborne nitrogen (nitrate and ammonium compounds) is in excess of these critical loads, this is termed an ‘exceedance’, and an ecosystem is considered at risk of eutrophication. The map shows areas where critical loads are not exceeded (grey shading), indicating no risk of eutrophication, and where atmospheric nitrogen deposition exceeds critical loads, by magnitude of exceedance.
Eq N ha-1 yr-1, nitrogen equivalents per hectare per year. 

Source: EEA (2022a).

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Reducing emissions of NH₃ to air will continue to be a significant challenge. For instance, 11 Member States failed to achieve their NH₃ reduction targets for 2020. The latest data on the distance to the 2030 emission reduction targets indicate that only five Member States are currently on track to achieve their national NH₃ targets (EEA, 2022b). Most Member States will need to significantly lower emissions to reach their 2030 commitments as explained. However, achieving the 2030 reduction targets for NH₃ will not prevent all impacts of eutrophication on ecosystems. Further reductions will be needed to achieve the long-term ambitions of the zero pollution action plan.

For marine habitats, nutrient loading in rivers is the primary source of eutrophication. However, air pollution deposition can also make significant contributions. Further efforts are needed to reduce key air pollutant emissions, such as emissions of NH₃ and NO_X, as explored further in the zero pollution ‘Signal’ on the significance of airborne nitrogen deposition to the Baltic Sea.

Acidification

Acidification in ecosystems can be caused by atmospheric inputs of sulphur and nitrogen. Adverse effects on, for example, freshwaters and forest soils result from a decline in the pH value — leading to toxic metal mobilisation — and from nutrient losses from, for example, agriculture. In turn, this can result in forest decline or increased fish mortality. However, as a result of emission reductions over recent decades (see Figure 10), acidification is now less detrimental across Europe than eutrophication.

Acidification in ecosystems can be caused by atmospheric inputs of sulphur and nitrogen. Adverse effects on, for example, freshwaters and forest soils result from a decline in the pH value — leading to toxic metal mobilisation — and from nutrient losses from, for example, agriculture. In turn, this can result in forest decline or increased fish mortality. However, as a result of emission reductions over recent decades (see Figure 10), acidification is now less detrimental across Europe than eutrophication.

Ozone and ozone precursors

Excessive levels of ozone cause damage to plants, reducing their growth and leading to poorer food crop yields. Ozone is formed in the atmosphere from chemical reactions between NO_X and volatile organic compounds (including methane). The primary way to reduce ozone levels is by controlling the emissions of these substances, otherwise known as ozone precursors. All ozone precursor emissions have declined over time, including emissions of NO_X, non-methane volatile organic compounds (NMVOCs) and methane, as shown in Figure 11. NO_X emissions reduced by 48% and NMVOC emissions by 31% between 2005 and 2020, while there was a more modest decrease in methane emissions of 17% over this period.  

Figure 11. Trends in emissions of NO_X, NMVOCs and methane in the EU-27, 2005-2020 (indexed to 2005)

Notes: NO_X = nitrogen oxides. NMVOCs = non-methane volatile organic compounds. CH₄ = methane.

Source: EEA (2022c).

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There is significant yearly variation in the percentage of EU agricultural land exposed to ozone levels above the EU’s long-term objective for vegetation. The percentage of agricultural land below the safe threshold of 6,000 μg/m³.hour has typically been 20% or less over the last 10 years (Figure 12). However, data suggest that reductions in ozone precursor emissions achieved to date have had little impact on crops’ exposure to ozone.  

Figure 12. Agricultural land exposed to ozone in the EU-27, 1996-2020

Notes: EU long-term objective for the protection of vegetation: 6 000 µg/m3.hour.  EU target value for the protection of vegetation: 18,000 µg/m³.hour (averaged over five years).

Source: EEA (2022d).

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Heavy metals

Heavy metals can be emitted from sources such as industrial activities and transport. Such pollutants present a risk to ecosystems because they can accumulate in soils, water habitats and sediments. Data on heavy metal emissions from EU Member States indicates that emissions of cadmium, mercury and lead have reduced significantly between 2005 and 2020 (EEA, 2022e). These developments are the result of EU actions taken to meet obligations under the Convention on Long-range Transboundary Air Pollution. From an industrial perspective, a significant proportion of the ecosystem impacts from heavy metals relates to emissions from a small number of installations involved in metal processing and fuel combustion (EEA, 2018b).

The zero pollution analysis on soils and ecosystems also shows how pollutants, including metals from other sources such as fertilisers (cadmium) and fungicides (copper), impact soil ecosystems. The zero pollution analysis on marine ecosystems includes information on the presence of hazardous substances in marine organisms.

Figure 13. Indicator analysis — air pollution and ecosystems

Note: Link to indicators: Exceedance of critical loads for eutrophication, Exposure of Europe’s ecosystems to ozone, Heavy metal emissions in Europe, Emissions of the main air pollutants in Europe.

Cover image source: © Panagiotis Dalagiorgos, Well with Nature /EEA