Air pollution reached hazardous levels across western Europe in June during a period of record-breaking heat, prompting health authorities to issue alerts. The UK experienced its third heatwave of the summer, with the London mayor issuing a rare high air pollution warning following extreme heat advisories issued from late June.
Ground-level ozone forms when other pollutants undergo chemical reactions in intense sunlight, creating a different hazard from the ozone layer in the upper atmosphere that shields against UV radiation. This tropospheric ozone poses serious health risks, including respiratory diseases, throat irritation, and worsening asthma symptoms. It also damages vegetation by causing browning and premature leaf loss. Historical precedent demonstrates the severity of such episodes: the 2003 European heatwave resulted in approximately 2,000 excess deaths in the UK, with roughly 800 attributed to ozone exposure, while the Netherlands experienced between 400 and 600 additional air pollution deaths.
Forecasts from the recent heatwave show ozone concentrations building throughout each day, typically peaking in late afternoon. Initial concentrations were highest over southern England, Belgium, northern France, and the Netherlands before shifting eastward. According to EU monitoring data, the most severe conditions appeared in Germany, the Benelux region, Italy’s Po valley, and localized areas in the Paris region, Spain, and Czech Republic, with concentrations described as notably elevated compared to previous years.
Ozone formation sources have shifted over time. While 1943 Los Angeles experienced some of the first recognized ozone smogs from traffic exhaust and petrochemical industry emissions, contemporary sources include pesticides, coatings, printing inks, adhesives, cleaning agents, and personal care products. In 2024, agricultural land covering nearly half a million square kilometers—representing 21.5% of Europe’s total—experienced ozone exposure above EU targets.
While peak ozone concentrations during the recent heatwave remained below those recorded in 1976 and 2003, overall ozone exposure trends lack clear direction. Addressing ground-level ozone requires coordinated international and national mitigation strategies, with climate change complicating efforts through increased wildfire frequency and intensity. Commitments such as the global methane pledge and stricter methane regulations offer potential benefits, though implementation requires sustained effort over time.