Over half of deaths attributed to ground-level ozone in Europe are due to ozone that originated outside the region

Ozone is formed in the level of the atmosphere closest to the earth (troposphere) from the reaction of sunlight with gases such as nitrogen oxides and volatile organic compounds. Although its presence in the upper layers of atmosphere can be protective, the presence of O₃ at ground level adversely affects human health, vegetation and ecosystems across Europe.

High levels are observed during the warm season and can cause a range of respiratory problems such as exacerbation of asthma, lower lung function and infections. Climate warming is likely to reinforce conditions conducive to the formation of tropospheric O₃ in the future, because the photochemical mechanisms of O₃ formation are favoured during heatwaves and periods of high solar radiation.

The European Union (EU) has set a limit of ozone levels of 120 micrograms per cubic metre (µg/m³) for the maximum daily eight-hour mean, whilst the WHO recommended guideline is at 100 µg/m3 per eight-hour mean. The revised EU ambient air quality directive, which entered into force in December 2024, includes the 100 µg/m³  limit as a long-term objective for 2050. 

The levels and concentrations of O₃ in a given location greatly depend on the transport of the pollutant itself within the lower levels of the troposphere. There is a lack of research on the deaths due to O₃ at a continental scale – in this case Europe – and on the geographical sources of the O₃ that causes these deaths. Both these insights are important to inform policy that works at a global level and can manage the health impacts of O₃ pollution. 

To assess the health impact of O₃ in Europe and how different sources contribute, researchers combined data on O₃ concentrations, population numbers and records of mortality, together with modelling data on the effects of O₃ on human mortality rates. A mortality rate in this study is the number of deaths per 1 million people for a specific year and geographic area. 

The region considered in the study includes 35 European countries and the surrounding ocean and sea. The data were analysed for 813 neighbouring regions in 35 European countries representing about 530 million people. Health data were obtained from Eurostat, and information on O₃ levels and its source were modelled from the CALIOPE air-quality system. The effect of O₃ on mortality was taken from the largest available multi-country epidemiological study to date¹.

The deaths attributable to O₃ for each country were analysed according to the source of origin of O₃ and classified into the following categories: 

1. National. 
2. The 34 other European countries. 
3. Other countries inside the study domain. 
4. Ocean and sea inside the study domain. 
5. Outside the study domain. 

There was variation between countries, both in terms of levels of O₃ and mortality rates. The average concentration of O₃ ranged from 76.7 µg/m³ in Finland to 130.1 µg/m³ in Malta. As expected, the concentrations of O₃ decreased northwards, as warmer temperatures in the south favour the formation of O₃, especially in summer.

The estimated number of deaths attributable to O₃ over the entire European domain considered in the study during the warm seasons of 2015–2017 was 114,447, resulting in mortality rate of 72 annual deaths per 1 million inhabitants. 

The highest estimated numbers of deaths from O₃ are for those countries with the largest populations such as Germany, Italy, France, the UK, Spain and Poland. Whereas the highest mortality rates (number of deaths per 1 million people) are in south-eastern countries such as Bulgaria, Serbia, Croatia, Hungary, Greece and Romania. 

The analysis found that only a small fraction: 11.7% of deaths from O₃ pollution, were due to national sources of the pollutant. Instead, it was O₃ transported from outside the European domain that was associated with the largest mortality burden and accounted for 56.7% of deaths. There was also a fair amount of O₃ related deaths within Europe, where 20.9% of mortality was due to O₃ from other European countries. The rest were from non-European countries (3.5%) and the ocean and sea inside the study domain (7.2%). 

The findings have implications for air-quality and public health policies across Europe. Previously, mitigation efforts have focused on national and regional scales. The researchers call for global strategies as well as co-ordinated pan-European actions to achieve the air-quality guidelines set out by the WHO and EU to reduce health impacts of O₃. They also warn that results should not be interpreted by local air-quality authorities as a justification for local inaction. 

In some coastal regions and smaller countries in the Mediterranean such as Malta, Greece and Cyprus, there was a considerable contribution to mortality from maritime transport  emissions (ships at sea). This indicates the need to implement a nitrogen emission control area for ships in the Mediterranean Sea (as previously established in the North Sea and Baltic Sea). This would help reduce nitrogen oxide (NOx) emissions from shipping which form O_3..

The researchers suggest that future work should refine the present study by analysing the contribution to mortality of the different economic sectors or activities, by country (for example: energy, industry, transport, residential and agriculture). This would help target interventions to the key sectors to improve air quality and drive new health policies.

Footnotes:

1. European Environment Agency (2020). Air quality in Europe 2020 report. Luxembourg: European Environment Agency.

Source: 

Achebak, H., Garatachea, R., Pay, M.T., Jorba, O., Guevara, M., Garcia-Pando, C.P. and Ballester, J. Geographic sources of ozone air pollution and mortality burden in Europe. (2024). Nature Medicine 30: 1732–1738. 

To cite this article/service:

“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by SCU, The University of the West of England, Bristol.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.