Association of short-term exposure to ozone with total and cause-specific mortality: A systematic review and...

Global ozone (O₃) levels have increased by 30-70 % over the past century, raising growing concerns about their impacts on human health under climate change. However, previous reviews have been regionally limited and lacked standardized exposure metrics or cause-specific analyses. To address these gaps, we systematically reviewed and quantitatively synthesized estimates from existing studies to evaluate associations of short-term O₃ exposure with total and cause-specific mortality. We identified 178 eligible time-series and case-crossover studies published up to August 2025, including 760 effect estimates across diverse regions. Exposure data were standardized to daily maximum 8-hour averages, and relative risks (RRs) corresponding to a 10 μg/m³ increase were pooled. With high certainty of evidence, short-term O₃ exposure was positively associated with total mortality (RR: 1.0033; 95 % CI: 1.0031-1.0036), cardiovascular mortality (RR: 1.0046; 95 % CI: 1.0042-1.0050), and respiratory mortality (RR: 1.0047; 95 % CI: 1.0040-1.0053). Heterogeneity was acceptable, and results were robust across sensitivity analyses. Potential nonlinear exposure-response relationships were identified, with thresholds ranging from 42.1 to 100 µg/m³. The estimated population attributable fractions of short-term O₃ exposure were 0.182 %, 0.252 %, and 0.258 % for total, cardiovascular, and respiratory mortality, respectively. Risk of bias was generally low to moderate. These findings highlight a measurable global health burden attributable to short-term O₃ exposure and provide the most up-to-date evidence supporting stricter O₃ air quality standards, particularly in low- and middle-income countries.