Population exposure to ozone and its gas-phase oxidation products in 25 European cities

Ozone and its oxidation products are increasingly recognized as significant health hazards. Understanding population exposure is critical for linking ozone and its products to health outcomes. This study used outdoor ozone concentrations from 47 monitoring stations and a Monte-Carlo approach based on mass balance model to assess exposures to ozone and 23 of its volatile oxidation products across 25 cities in 19 European countries (2015–2019), focusing on four age groups (15+ years). Average indoor concentrations of ozone and its oxidation products were 7.0 ppb and 24.6 ppb in residences, 12.5 ppb and 19.3 ppb in schools, and 12.7 ppb and 19.1 ppb in offices, respectively. Overall exposures averaged 10.9 ppb for ozone and 26.9 ppb for oxidation products, with oxidation product exposures exceeding ozone exposures across all age groups. Residences contributed 58.2% of ozone and 82.6% of oxidation product exposures due to lower air change rates and prolonged occupancy. These results highlight the significant role of residences in exposure, particularly for the elderly, and underscore the need for targeted indoor ozone mitigation strategies to protect public health.