Temporal changes in short-term PM2.5-cardiorespiratory mortality associations and implications for the health benefits of the clean air action in the Sichuan Basin, 2014-2022.

BACKGROUND: Evidence remains limited on how PM2.5-related mortality risk has evolved under sustained air-quality improvement following the implementation of the Clean Air Action (CAA), and how such changes have influenced related health benefits. This study aimed to investigate temporal changes in short-term PM2.5-related cardiorespiratory mortality associations and to quantify the respective contributions of PM2.5 concentration reductions and risk changes to mortality outcomes. METHODS: We conducted a multi-county time-series study in the Sichuan Basin, China, covering the period from 2014 to 2022. An extended two-stage analytical framework was applied to estimate county -specific PM2.5-mortality associations, followed by pooled analyses. Longitudinal meta-regression was used to assess annual trends in excess risk (ER), and period-specific analyses were performed across different stages of the CAA. Scenario analyses were conducted to quantify mortality changes attributable to PM2.5 concentration reductions and to temporal changes in the exposure-response relationship. RESULTS: A significant nonlinear temporal pattern in ER per 10 μg/m3 increase in PM2.5 was observed (P < 0.001), characterized by an increase during 2014-2016, a decline during 2017-2019, and an increase again during 2020-2022. Corresponding ERs for the three periods were 0.7% (95% CI: 0.6%-0.9%), 0.4% (95% CI: 0.3%-0.6%), and 1.4% (95% CI: 1.2%-1.6%), respectively. Declining PM2.5 concentrations were associated with 52,831 fewer cardiorespiratory deaths, whereas changes in ER increased mortality by 10,041 deaths. The later period increase in risk was consistently observed across sexes and was more pronounced among individuals aged 65 years and older. CONCLUSIONS: Temporal increases in short-term PM2.5-related mortality risk partially offset the health benefits achieved through reductions in PM2.5 concentrations during the later CAA period. These findings highlight the importance of incorporating time-varying health risk and population vulnerability into evaluations of air quality policies.