PM 2.5 , O 3 and survival gains from China’s clean air actions among patients with lung cancer: a 20-year registry-based cohort study in Beijing

Background In recent years, China has experienced declining fine particulate matter (PM 2.5 ) levels but rising ozone (O 3 ) levels. We aimed to examine the independent and joint associations of long-term exposure to PM 2.5 and O 3 with all-cause mortality among patients with lung cancer and to estimate potential survival gains. Methods We included 172 845 lung cancer patients diagnosed in 2003–2022 from the Beijing Cancer Registry. Three-year average pre-diagnosis PM 2.5 and O 3 were assigned using the ChinaHighAirPollutants dataset. Cox proportional hazards models were used to estimate associations of PM 2.5 and O 3 with mortality. Joint exposure-response patterns were examined using a two-dimensional tensor-product spline and quantified by the multiplicative interaction index. Model-estimated avoided deaths and extended expected lifespan (EEL) were calculated using counterfactual simulations based on 2013 exposure levels. Results Both PM 2.5 and O 3 were associated with increased mortality among patients with lung cancer, with HRs of 1.111 for PM 2.5 (95% CI 1.083 to 1.140) and 1.117 for O 3 (95% CI 1.070 to 1.166) per 10 μg/m 3 increase. A significant multiplicative interaction was observed between PM 2.5 and O 3 , with statistically significant positive interactions mainly occurring at higher O 3 concentrations (>105 µg/m 3 ). During 2016–2022, reductions in pre-diagnosis PM 2.5 exposure were associated with 13 229 model-estimated avoided deaths and a 7.8-month increase in 5-year EEL. However, O 3 and the PM 2.5 -O 3 interaction offset approximately 40% of these benefits. Discussion PM 2.5 reduction was associated with substantial survival gains among lung cancer patients, but rising O 3 and pollutant interactions partly offset these benefits, supporting coordinated multipollutant control.