Geographic sources of ozone air pollution and mortality burden in Europe

Ground-level ozone (O3) is a harmful air pollutant formed by sunlight-driven reactions of precursor gases. Europe’s current O3 levels are a major source of premature mortality, yet mitigation actions have mainly been national or regional, lacking a comprehensive assessment of geographic sources and related health impacts. This study quantifies national and imported contributions to O3 and the associated mortality across 813 contiguous regions in 35 European countries (~530 million people). Imported O3 contributed to 88.3% of all O3-attributable deaths (intercountry range 83–100%). The largest imported share originated outside the study domain (hemispheric sources), responsible for 56.7% of total O3-attributable mortality (range 42.5–87.2%). Achieving WHO air-quality guidelines and avoiding O3-related health impacts require not only national or pan-European actions but also global strategies.