Source-specific short-term-ozone exposure and specific cancer mortality risk: A multi-country study in 11,215 communities.

Ozone (O) exposure is a recognised risk factor for respiratory and cardiovascular mortality, but its short-term effects on cancer remain largely unknown due to the absence of large-scale, multi-country evidence. Based on 9233,612 cancer deaths from 2000 to 2019 across 11,215 communities in Australia, Brazil, Canada, Chile, South Korea, Mexico, New Zealand and Thailand, this study provides the first comprehensive multi-country assessment of the associations between short-term O exposure and mortality from a wide range of cancer types, together with the contributions of major emission sources. Daily maximum 8-hour O concentrations were linked to residential locations and analysed using a space-time-stratified case-crossover design, with source-specific contributions from traffic, landscape fires and industrial emissions quantified. Each 10 μg/m increase in O (lag 0-1 days) was associated with a 0.84% (95% CI: 0.77-0.91%) increase in all-cancer mortality, with elevated risks observed for 24 cancer types except for nasopharyngeal, testicular cancer, and leukemia. Effect estimates varied by cancer type, ranging from a 0.42% increase for liver cancer to a 1.43% increase for thyroid cancer per 10 μg/m rise in O exposure. Short-term O exposure accounted for 6.37% (5.84-6.91%) of all cancer deaths, with the largest attributable fractions in Brazil (10.8%), Chile (6.3%) and Thailand (6.0%). Traffic emissions were the dominant contributor to O-attributable cancer deaths overall, while landscape fire-related O contributed substantially in Australia and Brazil. These findings reveal a significant and previously under-recognised short-term impact of O exposure on cancer mortality and identify key emission sources driving this burden. The results provide important evidence for air-quality management and targeted cancer prevention strategies in diverse global regions.