Premature deaths linked to long-term exposure to ground-level ozone nearly doubled worldwide between 2000 and 2020, reaching an estimated 480,000 deaths annually, according to a new global assessment led by researchers at George Washington University.
The study, published as part of the Tropospheric Ozone Assessment Report, Phase II (TOAR-II), provides the most comprehensive assessment to date of global trends in long-term ozone exposure and its health impacts. It does so through use of a first-of-its-kind global database created for TOAR-II that compiles ozone observations from thousands of sites across the world. Ground-level ozone is a harmful air pollutant that forms when emissions from vehicles, power plants and industrial facilities chemically react in sunlight and heat. The study's author team includes over twenty leading global scientists specializing in ozone pollution and health impacts.
Researchers found that ozone levels and associated health burdens have declined in parts of North America and Europe, driven by controls on nitrogen oxide emissions from vehicles and industry, cleaner fuels, and technological transitions. Meanwhile, they have increased substantially across much of the Global South, which is rapidly industrializing.
"Ozone pollution remains an important global health threat, and the burden is shifting toward regions that often have the fewest resources to monitor and address it," said Gaige Kerr, lead author and assistant professor in the Department of Environmental and Occupational Health at the George Washington University Milken Institute School of Public Health. "Our findings show that reducing ozone precursor emissions can protect health, but we need much stronger monitoring and pollution controls in regions where ozone exposure is rising."
Findings
Ozone exposure is rising in many parts of the world: Researchers analyzed global ozone observations and modeled estimates from 2000 to 2020, focusing on two health-relevant measures of long-term exposure. They found the highest recent ozone concentrations in South Asia, eastern China and parts of the Middle East and North Africa.
Major gaps in global monitoring: Despite a 32% increase in monitoring since the first TOAR assessment, major gaps remain. The TOAR-II database included 6,335 monitors across just 59 of 225 countries and territories. About 3 billion people - 38.6% of the global population in 2020 - lived in countries without adequate monitoring represented in the database. The largest gaps are in South Asia and Sub-Saharan Africa.
Climate change threatens to reverse progress on reducing ozone: Climate change is expected to alter the atmospheric conditions that govern ozone formation and transport, potentially driving future burdens high. Studies project that without ambitious greenhouse gas and emission reductions, ozone-attributable deaths could reach 2-3.5 million annually by 2100 - several times higher than today.
The assessment's author team additionally uses its collective expertise to discuss evidence on how ozone harms human health and evaluate methods to quantify health impacts from ozone exposure. The author team also calls for expanded ozone monitoring, improved health and epidemiological data, better exposure modeling and sustained reductions in ozone precursor emissions.
The study will be published on October 26, 2026 in Philosophical Transactions of the Royal Society.