Impacts of air pollution on ecosystems in Europe

Overview of harmful impacts from air pollutants

Air pollution negatively impacts both terrestrial and aquatic ecosystems, degrading environments and reducing biodiversity. Various pollutants harm ecosystem health in different ways.

O₃ is a secondary air pollutant, formed when other pollutants known as precursors (nitrogen oxides (NO_X) and volatile organic compounds including methane) react in the atmosphere in the presence of sunlight. It damages agricultural crops, forests and plants by reducing growth rates, lowering yields, and affecting biodiversity. Reduced wheat and potato yields demonstrate ozone’s negative impact, with estimated losses in 2022 of EUR 1.3 billion for wheat and EUR 680 million for potatoes across Europe.

Nitrogen deposition, on land and in water bodies, is mainly caused by ammonia (NH₃) from agricultural activities and NO_X from combustion processes. Excessive amounts of nitrogen introduced to an ecosystem lead to several negative impacts. In water bodies, it contributes to eutrophication, characterised by algal blooms and less available oxygen due to excess nutrients. In sensitive terrestrial ecosystems such as grasslands, if critical loads for nitrogen deposition are exceeded, sensitive species can be lost. In tandem, species that benefit from high nitrogen levels can flourish, which can change the structure and function of an ecosystem.

SO₂ can also bring significant negative impacts to ecosystems. The deposition of SO₂, as well as NO_X and NH₃, can lead to changes in the chemical composition of soils, lakes, rivers and marine waters. This can cause acidification, which disrupts ecosystems and leads to biodiversity loss. The main sources of SO₂ are industry and energy supply (EEA, 2024a).

Heavy metals are toxic pollutants that travel long distances in the atmosphere and are deposited into ecosystems. They build up in soils and subsequently bioaccumulate (i.e. a substance builds-up within an organism over its lifetime) and bio-magnify in the food chain (i.e. the concentrations of substances in the tissue of animals increases progressively through the food web). The main sources of heavy metals include manufacturing and extractive industries, energy supply and road transport (EEA, 2024a).

The EEA report on Europe’s state of water identifies that ‘Europe's waters continue to be impacted by chemicals, predominantly by atmospheric pollution from coal-powered energy generation and diffuse pollution from agriculture’ (EEA, 2024c). Countries report that the main pollution pressures on surface waters are linked to pollution from diffuse sources such as atmospheric deposition (52%).

Air quality standards to protect vegetation

The Ambient Air Quality Directives set standards to protect vegetation from air pollution, including a target value and a long-term objective for ozone, and critical levels for NO_X and SO₂. The 2024 revised Ambient Air Quality Directive restates the previously agreed standards to protect vegetation from air pollution and national obligations for minimum numbers of monitoring sites. It also introduces standards which are more closely aligned with the World Health Organization’s recommendations to protect human health.

Risk assessments and assessments of compliance with critical levels to protect vegetation focus most on rural areas. As stated in the revised Ambient Air Quality Directive (EU, 2024) such  assessments should also consider and complement requirements in the National Emission Reduction Commitments Directive to monitor the impacts of air pollution on terrestrial and aquatic ecosystems, and to report on such impacts regularly.

Under the Convention on Long-Range Transboundary Air Pollution, referred to as the UNECE Air Convention, a critical ozone exposure level for the protection of forests is also defined.

The various standards are presented in Table 1.

Exposure of vegetation to ground-level ozone

O₃ enters plant leaves and reduces photosynthesis, slowing a plant’s growth and increasing its vulnerability to pests and disease. At the ecosystem level, high levels of O₃ can drive the loss of species diversity, change the structure of an ecosystem and impact habitat quality. In commercial agriculture, O₃ reduces crop yields and forest growth.

The Ambient Air Quality Directive (EU, 2008) aimed to protect vegetation from O₃ by implementing two standards: a target value that should have been met by 1 January 2010 and a long-term objective, with no defined attainment date. The 2024 revised Air Quality Directive (EU, 2024) sets 1 January 2050 as the deadline for attaining the long-term objective.

Figure 1 presents modelled estimates of the percentage of total agricultural land exposed to O₃ above the threshold value of 18,000µg/m³ per hour from 2000 to 2022 in the 32 EEA member countries (EEA-32).

A substantial proportion of the total agricultural area in the EEA-32 is exposed to O₃ levels above the threshold. Exceedances have been observed regularly in central, southern and eastern Europe over time. It is hard to identify particular trends since there is considerable variation on the exposure to O₃ levels from year to year, partially due to differing meteorological conditions, but the underlying indication is that the target value for protecting vegetation is being exceeded less commonly over time.

In 2022, O₃ levels exceeded the target value threshold in 32.5% of the total agricultural area in the EEA-32. This was higher compared to the two previous years, something which could have been related to the meteorological influence on O₃ formation. According to the Copernicus Climate Service (Copernicus Atmosphere Monitoring Service, 2023), 2022 was the fifth warmest year on record globally and the second warmest year in Europe. The summer of 2022 was the warmest summer in Europe on record at the time. Heatwaves lead to warm and cloud-free conditions which enhance O₃ formation, and climate change will increase the frequency and intensity of such events.

The long-term objective for vegetation protection set in the Ambient Air Quality Directive is 6,000µg/m³ per hour. This is in line with the critical level for ozone for the protection of crops, as defined by the UNECE Air Convention. In 2022, only 11.2% of the total agricultural area of the EEA countries met this long-term objective. Where the critical level is exceeded, there is an increased risk of damage to vegetation as a result of O₃ exposure.

Under the UNECE Air Convention, the critical O₃ exposure level for the protection of forests is 10,000μg/m³ per hour. Concentrations above this critical level potentially have direct adverse effects on plants and ecosystems. Despite significant annual variation, more than half of the total forested area across the EEA-32 has been exposed to O₃ levels above the critical level every year since 2005 (Figure 2). In 2022, only 38% of the total forest area was below this critical level.

Figures 1 and 2 are based on modelled information. When focusing only on air quality monitoring stations, data from rural background air quality stations in 2022 show that 56% of the stations that reported data registered values above the target value threshold. Moreover, 90% of rural background stations measured values above the long-term objective.

Wheat and potato yield loss due to exposure to O₃

O₃ damages agricultural crops, affecting the quality and yield of production and resulting in significant economic losses for the sector. This section of the briefing discusses calculated percentage losses in wheat and potato yields due to O₃ exposure as well as estimated monetary losses across EEA countries. Other crops may be affected by exposure to O₃ but these are not quantified here due to limited data availability.

As a reference point for interpreting the percentages, in 2023, the EU harvested 125.9 million tonnes of common wheat and spelt, and 48.1 million tonnes of potatoes (Eurostat, 2024). While this section of the briefing discusses reduced yield for both wheat and potatoes, Figures 3 and 4 focus on the calculations for potatoes, first made available in 2021.

Maps which show percentages of wheat yield losses, at the national and regional levels, are available in the European Topic Centre (ETC) report on wheat and potato yield loss in 2022 in Europe due to ozone exposure (ETC HE, 2024). The highest wheat yield losses in 2022 were estimated in Belgium (7.3%), France (6.9%), Czechia (6.6%) and Spain (6.4%). In fact, wheat yield losses exceeded 2% in 19 countries. The countries with the highest production of wheat in 2022 were France, Germany, Türkiye, Poland, Belgium and Spain.

Around 6.7 million tonnes of wheat, equivalent to EUR 1.3 billion, were estimated to be lost in 2022 due to the impact of ground-level ozone across Europe. The significance of the losses varies across regions, depending on the level of O₃ and the absolute production of the respective crop. Losses were highest in France (EUR 490 million) and Germany (EUR 273 million).

Figure 3 presents the percentages of potato yield losses due to O₃ exposure at the national level in 2022. These equated to 10% in Czechia, 8.9% in Slovenia, 8% in Germany and 7.1% in France. Potato yield losses exceeded 4% in 17 countries. The countries with the highest production of potatoes in 2022 were Germany, France, the Netherlands, Poland, Türkiye and Belgium, indicating that the higher yield losses do not always affect the largest producers.

Figure 4 shows the estimated economic losses relating to potatoes due to O₃ by country. In 2022, production and economic losses for potatoes amounted to around 3.2 million tonnes or EUR 680 million. The countries which experienced the highest production losses were Germany (EUR 197 million), France (EUR 130 million), the Netherlands (EUR 94 million) and Poland (EUR 76 million). On a country-by-country basis, economic losses exceeded EUR 10 million in 16 countries for wheat and in 12 countries for potatoes.

While the calculated impacts of O₃ in 2022 are significant in terms of the quantities involved and economic losses, they are lower than in previous years. This is directly related to the fact that the level of O₃ can vary significantly from year to year as shown in Figure 1.

Eutrophication due to nitrogen deposition

Nitrogen is present in the air in different forms, including as nitrogen monoxide, nitrogen dioxide and ammonia. The atmospheric deposition of nitrogen in terrestrial ecosystems can cause harmful eutrophication when critical loads are exceeded. The critical load refers to a threshold below which the ecosystem can absorb pollutants deposited from the atmosphere without disruption. Deposition above this threshold is likely to disrupt terrestrial and aquatic ecosystems and lead to changes in species diversity. Critical loads are different for different ecosystem types. Overall exceedances are estimated using modelling methods.

The ZPAP aims to reduce pollution in the EU to levels not harmful to human health or ecosystems by 2050. Interim targets are also set for 2030, including the objective to reduce the area of ecosystems where nitrogen deposition exceeds critical loads by 25% by 2030 compared to the levels in 2005. The EEA has developed an indicator to monitor progress in reducing eutrophication due to nitrogen and reaching the zero pollution target.

This objective is currently unlikely to be met as the total area where nitrogen deposition exceeded the critical loads for eutrophication fell by 13% between 2005 and 2022, with 73% of the area of EU-27 ecosystems remaining above the critical loads for nitrogen in 2022.

Since 2005, the critical loads for nitrogen were exceeded in almost all EU Member States. The exceedances are attributed to both nitrogen compounds from agricultural activities (as NH₃) and nitrogen from combustion processes (as NO_X).

In 2022, the highest exceedances of nitrogen critical loads were found in the Po Valley in Italy, on the border areas between the Netherlands and Germany, along the border between Denmark and Germany, and in north-eastern Spain (EMEP, 2024).

The Forest Condition in Europe 2023 report states that there was high throughfall deposition, of inorganic nitrogen observed throughout central Europe in 2021, with high ammonium depositions being found in a wider area than high nitrate depositions across the International Cooperative Programme (ICP) Forests intensive monitoring plots (ICP Forests, 2023).

Acidification 

The deposition of SO₂, NOx and a NH₃ leads to changes in the chemical composition of soils, lakes, rivers and marine waters, resulting in acidification. The impacts of low pH values on freshwater and forest soils include the release of toxic metals and a loss of nutrients, resulting in fish mortality and forest decline, respectively.

Significant decreases in SO₂ emissions over recent decades have successfully addressed the problem of acidification. Between 2005 and 2022, SO_x emissions decreased by 81% in the EU-27 (EEA, 2024b). The European Monitoring and Evaluation Programme (EMEP), which models deposition data, estimates that exceedances of critical loads for acidification due to nitrogen and sulphur were found in only 3.3% of European terrestrial ecosystems in 2022 (EMEP, 2024). Hotspots occurred in the Netherlands and its borders with Germany and Belgium, and in small parts of southern Germany and Czechia.

Exposure of vegetation to NOx and SO₂ above critical levels

Exposure of vegetation to NOx and SO₂ can be assessed on the basis of monitoring data reported to the EEA in accordance with the Ambient Air Quality Directive (EU, 2008).

Ambient air concentrations can be compared to ‘critical levels’, which represent a threshold for gaseous NOx in ambient air.

The annual critical level for protecting vegetation from exposure to NOx (an annual mean of 30μg/m³) was exceeded in 2022 at only 6 out of 393 reporting rural background stations: one in Italy, one in the Netherlands and four in Türkiye (see EEA annual air quality statistics).

The EEA’s interpolated maps for 2022 indicate that in most of Europe, NO_x levels are below the critical level for protecting vegetation. However, annual mean NO_x concentrations were estimated to be above the critical level for the protection of vegetation in the Po Valley, part of the Netherlands and Belgium, the German Ruhr area and around some larger European cities; this is likely a result of high emissions from transport in and around the cities, as well as energy production and industrial sites in those areas (ETC HE, 2024b).

The critical level for SO₂ (an annual mean of 20μg/m³) was exceeded at one station in Bosnia and Herzegovina out of the 287 rural background stations that reported data for 2022. The critical level for winter was not exceeded at any of the 287 rural background stations that reported these data (see EEA annual air quality statistics).

Heavy metals

Heavy metals emitted to air are transported long distances in the atmosphere and deposited into ecosystems. Heavy metals are toxic to human health, animals and plants; they persist in ecosystems, leading to their bioaccumulation in the food chain. In addition, the deposition of heavy metals in marine waters contributes to the presence of metals in marine organisms. Between 2010 and 2021, nine hazardous substances, including cadmium, lead and mercury, were monitored in marine organisms, all exceeding safe limit values set to protect human health as reported by the EEA in 2024.

An analysis of heavy metal concentrations in EU agricultural soils (JRC, 2024) under the sewage sludge directive found that 19% of samples exceeded the limit values for at least one single heavy metal. The distribution of heavy metals in agricultural soils was recently documented in a report by the ETC for Data Integration and Digitalisation (ETC DI, 2023), with exceedances seen across a significant proportion of Europe’s agricultural areas. Atmospheric deposition contributed significantly to lead (47%) and cadmium (31%) levels in agricultural soils.

According to the recent report on Europe's state of water, atmospheric deposition also contributes to widespread mercury contamination with 49% of surface waters affected by mercury.