Associations of green and blue spaces with life expectancy are partly explained by lower ambient particulate matter: Evidence from 1898 Chinese counties over two decades

Introduction While green and blue spaces (GBS) may support population health, the pathways linking GBS to life expectancy remain inadequately quantified. Objectives We aimed to examine the extent to which the association between GBS and life expectancy is statistically explained by specific size fractions of ambient particulate matter (PM). Methods We conducted a study covering 1,898 counties in five major regions of China from 2000 to 2021. Life expectancy data were obtained from national registries. GBS exposure was defined by the joint distribution of both green and blue space coverages. PM exposure, including PM 1 , PM 1-2.5 , and PM 2.5-10 , was derived from high-resolution datasets. By integrating generalized additive mixed models within a mediation analysis framework, we decomposed the total effect between GBS and life expectancy into direct and indirect effects. Results For a simultaneous ten percentage point increase in both green and blue space coverages, the total effect was 0.968 years (95% CI : 0.945 to 0.991). Lower PM concentrations statistically explained approximately 23% of this association. PM 1 contributed the most (0.109 years, 0.095 to 0.123), followed by PM 2.5-10 (0.065 years, 0.060 to 0.071) and PM 1-2.5 (0.050 years, 0.043 to 0.055). The indirect effects varied across regions, with the strongest effect in Northwest China and the weakest in East China. The total indirect effect in underdeveloped regions was approximately twice that in developed regions. Conclusion A substantial proportion of the positive association between GBS and life expectancy could be explained by PM reductions, with PM 1 contributing the most to this association. The indirect associations varied across regional and socioeconomic contexts. GBS planning may therefore need to consider local conditions and could complement direct emission reductions.