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• Healthy ageing is a process of developing or maintaining the functional capability. • Find out linear and non-linear effects of clean air policy on functional capacity. • Long-term exposure PM 2.5 was applied as a proxy of clean air policy. • The subpopulations possibly modify the effects of air pollution. • Different influencing mechanism of air pollutant on outdoor and indoor activities. Since there is limited knowledge about health effects of the clean air policy (CAP, i.e., a series of emission-control actions) on continuum functional capacity (CFC) among the older adults on a large representative data, our research was to fill this gap. We used a continuous variable of airborne fine particulate matter (PM 2.5) particles as a proxy for the CAP to evaluate the linear and non-linear effect of PM 2.5 exposure on CFC of older adults, under the quasi-experimental framework of the temporal contrast between 2011 (before the CAP) and 2015 (after the CAP). Multiple environmental factors were considered and spline function was utilized to fit the spatial autocorrelations. A competing risk model was constructed to qualify the impact of PM 2.5 on multidimensional disability. After adjusting for potential confounders, a J-shaped association was found between PM 2.5 concentration increase on CFC, with a threshold 2μg/m3. We also demonstrated that a 10-µg/m3 increase in PM 2.5 concentration was related to a 14.0% (95% CI :0.00, 19.00%) increment risk in the functional decline. Similarly, the competing risk model presented a hazard ratio of multidimensional disability ranging from 1.707(0.928-4.141) at 40μg/m3 concentration of PM 2.5 to 4.384 (1.970-9.755) over 80μg/m3. Stratified analyses showed that married men less than 80 years old in rural areas are more likely to be affected by PM 2.5 exposure, where the influencing mechanism of air pollutant to outdoor and indoor activities might be the potential cause. Implementing CAP might improve CFC, prevent the occurrence of disability, and update the air policy. [ABSTRACT FROM AUTHOR]