Associations of ambient PM2.5 and O3 with cardiovascular mortality: a time-series study in Hefei, China.

China is among the countries with the worst air quality throughout the world. As PM2.5 was not included in the national air quality monitoring network before January 2013 in China, no study has investigated the associations of ambient PM2.5 and O3 with cardiovascular mortality in Hefei, China. In this time-series analysis, Poisson regression in generalized additive model was adopted to assess the associations between the air pollutants and cardiovascular mortality during the 2013-2015 in Hefei, China. The findings showed that the daily average level of PM2.5 and O3 was 77.8 μg/m3 and 60.1 μg/m3 in the study period, respectively. PM2.5 and O3 exposure tended to increase cardiovascular mortality, but the associations were statistically insignificant. Further stratified analyses by seasons showed that with every 10 μg/m3 increase of PM2.5 in the cold season (October-March), the risk of cardiovascular death increased by 0.22% (95% CI 0.05%, 0.39%); while every 10 μg/m3 increase of O3 in the warm season (April-September), the risk of cardiovascular death increased by 1.29% (95% CI 0.26%, 2.33%) on Lag0. Interestingly, stratified analysis by gender showed that the associations of PM2.5, but not O3 exposure, could significantly increase cardiovascular mortality in females, but not males. The findings of this study especially underscored the adverse associations of PM2.5 and O3 exposure with females in specific seasons. More studies are needed to verify our findings and further investigate the underlying mechanisms. Graphical Abstract.