Heatwaves and wildfires, combined with human-caused emissions, exposed about one third of the world's population to extremely high levels of ground-level ozone pollution in 2026, according to a report published on Wednesday by the European Union's Copernicus Atmosphere Monitoring Service (CAMS). The analysis covers January 1 to September 15 and found that 34 percent of people worldwide breathed air rated "extremely poor", meaning ozone concentrations were well above World Health Organization (WHO) guidance. Another 17 percent breathed "very poor" air, while only five percent were exposed to "good" levels. French broadcaster RFI, citing the same data, put the share of people exposed to dangerous levels at close to 40 percent, a difference that likely reflects how the categories are grouped.

This ozone is not the protective layer high in the atmosphere. It forms near the ground when heat and sunlight react with emissions from vehicles, industry and wildfires. It can damage lung tissue, cause breathing problems and trigger asthma attacks, and it also harms ecosystems and crop yields. The WHO recommends a maximum of 100 micrograms per cubic metre, averaged over eight hours.

Asia was the worst affected region. CAMS says 53 percent of its population breathed "extremely poor" air, with a further 22 percent exposed to "very poor" levels; RFI reported a figure of 60 percent for extremely high levels. New Delhi, Dhaka, Chongqing in China and Lahore in Pakistan were among the cities with extremely poor readings, driven by industrialisation, transport, wildfires and agricultural burning. In North America, two thirds of people were exposed to "poor" or "very poor" air, as were 45 percent in Europe. Ozone is linked to around 60,000 premature deaths a year in Europe, said Ian Marnane of the European Environment Agency. Eight percent of Africans faced extremely poor air, and Oceania fared best, with 66 percent enjoying good levels. In South America, Sao Paulo had very high levels and Rio de Janeiro extremely elevated ones, though 81 percent of the continent's people had good or fair air.

The report points to record heatwaves and wildfires in Europe and North America this year, with smoke carried well beyond their borders. Indonesia has also seen major fires, and the El Niño weather pattern, which began in June and is due to peak later this year, could fuel more fires in southeast Asia. Spain's El País reported that Copernicus has for the first time mapped cross-border pollution, including ozone, Saharan dust and wildfire smoke, and places Spain in Europe's most problematic zone.

The findings matter because ozone has resisted the progress made on other pollutants. EU regulation has cut most air pollutants except ozone, and levels in North America stayed "relatively unchanged" despite ambitious policies. As CAMS director Laurence Rouil put it, "Air pollution does not stop at borders. It can travel thousands of kilometres, crossing continents and oceans." Because warming favours ozone formation, the report highlights how climate change and air quality are closely tied.