A new global report reveals that billions of people faced unhealthy ground-level ozone pollution in 2026, with Asia experiencing the worst exposure.
The ozone most people have heard of sits miles overhead and blocks the sun’s ultraviolet light.
The same gas also forms near the ground when pollutants from vehicles, factories and other sources react in sunlight.
Down there it irritates lungs instead of protecting them.
A new analysis from Europe’s atmosphere monitoring service estimates that only 5 percent of the world’s people breathed ozone at a level the World Health Organization calls good this year.
Almost 40 percent were exposed to the highest category the service tracks, and Asia was hit hardest. The figures come from a global model fed with satellite and ground readings, not from a monitor outside every home.
The Copernicus Atmosphere Monitoring Service, or CAMS, is run by the European Centre for Medium-Range Weather Forecasts (ECMWF) for the European Commission.
Its new report, Atmosphere Watch, covers ozone, wildfire smoke and desert dust from January 1 to September 15.
Laurence Rouil directs CAMS. In written answers sent to Earth.com through the Copernicus press office, Rouil said the year’s surprise was how many big pollution events piled up at once.
“When we brought together the huge amount of data produced every day by CAMS, the most striking finding was that more than half of the world’s population was still exposed to unhealthy levels of air pollution,” Rouil said.
Nothing emits ground-level ozone directly. Nitrogen oxides from burning fuel react in sunlight with organic vapors from traffic, industry, household solvents, plants and wildfires.
Hot, still summer weather speeds the reactions and lets the gas build up.
Ozone lasts a few days near the ground and a few weeks higher up. That is long enough to drift across borders and oceans.
During the heatwave of July 28, CAMS calculated that ozone arriving in Bergamo, Italy, from elsewhere in the Northern Hemisphere mattered as much as every human source in Europe combined.
The report measures exposure the way the World Health Organization does. It takes each day’s highest eight-hour ozone reading and averages it over the six worst months of the year.
The WHO guideline is 60 micrograms per cubic meter. Above 110, CAMS calls the air extremely poor, and that is the band almost 40 percent of people fell into.
CAMS estimates that six in ten people in Asia experienced extremely poor ozone levels, while nine in ten experienced air rated poor or worse.
Delhi, Cairo, Milan, Mexico City and Rio de Janeiro had some of the highest exposure on their continents.
Europe has cut every pollutant its air quality law regulates except ozone, the service’s annual assessments show. This summer’s repeated heatwaves pushed half of Europeans into poor air or worse.
European ozone standards limit how often concentrations can exceed 120 micrograms per cubic meter, and much of the continent struggled with elevated levels.
In North America, more than two thirds of people breathed poor ozone or worse, mostly on the two U.S. coasts and in big cities.
Decades of emission cuts have left ozone there largely unchanged, the report says, partly because wildfires supply the ingredients.
Oceania, South America and much of Africa did far better. Everyone in Oceania, 81 percent of South Americans and 56 percent of Africans had good or fair ozone levels.
On July 22, fires in France’s Gironde and Landes regions burned close to 124,000 acres (50,000 hectares) and forced 40,000 people from their homes.
Their smoke fouled the air hundreds of miles away. Fires near Ávila and Madrid in Spain burned a similar area and sent 56,000 people fleeing.
Belgium’s High Fens fire in August was the country’s largest in a century, and its smoke crossed Germany into Poland.
In July, wildfire smoke from Canada’s Northwest Territories and Ontario spread over the northern United States.
Cities from Chicago to Philadelphia issued air advisories days before the World Cup final in New Jersey, and storms washed the air clean just before the match.
In Indonesia, peat fires on Borneo, fed by a building El Niño, pushed fine particle levels to several hundred micrograms per cubic meter.
Saharan dust crossed the Atlantic toward the Caribbean, and the Canary Islands topped Europe’s list of cities with dust alerts.
Asked by Earth.com what someone in a high-ozone region should do on the worst days, Rouil pointed to the WHO.
Ozone forecasts are now widely available and increasingly reliable, Rouil said, so people can act before an episode peaks.
“WHO advises reducing prolonged or intense outdoor physical activity, especially in the afternoon,” Rouil said.
Further guidelines recommend that children, older adults, and people with respiratory or cardiovascular conditions take extra precautions, he told Earth.com.
The director also said that the fixes are known. Decades of European rules have brought down sulfur dioxide, fine particles and nitrogen dioxide, Rouil said, and the job now is to keep that momentum.
The exposure figures are model estimates rather than direct measurements at every location.
CAMS combines satellite and ground observations with a model that tracks more than 50 chemicals, then matches the results to population maps.
A model fills the gaps where no monitor stands, but it isn’t the same as a sensor on the street outside.
The report stops at September 15 and doesn’t count deaths from this year’s ozone. For scale, the WHO estimates that outdoor air pollution causes more than 4 million early deaths a year.
The Health Effects Institute’s State of Global Air report finds ozone exposure in Asia has risen in recent years.
How much of Europe’s summer ozone came from its own wildfires is still an open question, and CAMS says it is actively researching it.
With a strong El Niño building and fires already burning in Indonesia, the service expects more fires to make headlines in the months ahead.
Atmosphere Watch 2026 is a monitoring report published by the Copernicus Atmosphere Monitoring Service on September 30.
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