Copernicus: High temperatures trigger seasonal ozone pollution across Europe

Forecasts from the Copernicus Atmosphere Monitoring Service (CAMS) are showing increased surface ozone concentrations across a large part of Europe amid increasing summer heatwaves. The exceedance of the ozone concentrations above the threshold values set by the European Ambient Air Quality Standards poses significant health and environmental risks.

CAMS scientists pay particular attention to surface ozone pollution during the summer months, when higher temperatures and anticyclonic weather patterns provide favourable conditions for ozone pollution to accumulate. Since the start of the summer, CAMS has monitored several periods conducive to an increase in surface ozone concentrations. With the recent increase in temperatures and heatwaves a new episode of high surface ozone concentrations, and exceedances of limit values set by the European air quality legislation in several areas in Western and Southern Europe, has been forecast between 29 July and 4 August. In particular, surface ozone concentrations with peak values are forecast for the Paris region, Benelux, and Germany, highlighting the significant role played by precursor emissions (nitrogen oxides and volatile organic compounds) which are often emitted far from the locations where the pollution episodes take place. The Po Valley in northern Italy is also predicted to experience very high surface ozone concentrations during these days.

Ground level ozone is an air pollutant that contributes to poor air quality. One health impact of ozone is through lung inflation which, in addition to the heat stress during the summer, can create critical conditions, especially for those with existing health conditions.

According to the European Directive on Ambient Air quality, the maximum daily eight-hour mean of ozone levels must be below 120 µg/m3, with an exceedance permitted of 25 days per year (18 days in the revised ambient air quality directive adopted by the European Parliament in April 2024).

In addition to the adverse effects on human health, surface ozone concentrations have also harmful impacts on vegetation and ecosystems and can also seriously affect crop yield and be responsible for loss of biodiversity.

Episodes of high ground-level ozone concentrations are influenced by emissions of precursors and high temperatures and solar radiation, therefore could be more frequent with the rising number of heatwaves and rising temperatures (this is the “climate penalty effect”). Another characteristic of ozone is its long lifetime in the atmosphere so that the ozone levels in some areas are also influenced by long range transport of air pollution. The CAMS 2023 European air quality interim annual assessment report describes the clear correlation between the extremely warm temperatures and high surface ozone levels, and the need to mitigate emission sources both at the local and the global scales. The report gives also some insights to understand the seasonality of these episodes.

Laurence Rouil, Copernicus Atmosphere Monitoring Service (CAMS) Director, said: "Accurate forecasting and understanding the long-range transport of ozone is vital. As temperatures rise due to changing climate, our ability to predict and respond to these episodes becomes increasingly crucial to provide timely alerts, enabling authorities to respond promptly with appropriate measures to mitigate health risks and environmental impacts."

More about how this summer pollutant works here. To know more about which sectors contribute to ozone pollution in Europe’s major cities, you can go visit CAMS’ website.

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