The Interactive Effects of Extreme Temperatures and PM2.5 Pollution on Mortalities in Jiangsu Province, China

Background: Exposure to either extreme temperatures or fine particles (PM 2.5 ) is associated with adverse health outcomes but their interactive effects remain unclear. Here, we aimed to explore the interactions of extreme air temperatures and PM 2.5 pollution on total and cause-specific mortalities. Methods Based on the daily mortality data collected between 2015 and 2019 in Jiangsu Province, China, we conducted generalized linear models to estimate the regional-level independent effects of cold/hot extremes and PM 2.5 pollution. We further evaluated the relative excess risk due to interaction (RERI) to represent the combined effects. We estimated the joint effects with different extreme temperatures and PM 2.5 pollution cutoffs. Results The relative risks (RRs) of total and cause-specific mortality associated with hot extremes were significantly stronger ( p  < 0.05) than those related to cold extremes across three regions in Jiangsu; the associations with cold extremes were less consistent. We identified significantly higher interactions ( p  < 0.05) between hot extremes and PM 2.5 pollution than those between cold extremes and PM 2.5 pollution, with RERIs ranging between 0.00 and 1.15 in hot seasons. The joint effects peaked on ischaemic heart disease (RERI = 1.13 [95%CI: 0.85, 1.41]) in middle Jiangsu. For respiratory mortality, RERIs were higher in females and in the less educated. The interaction pattern remained consistent when defining the extremes/pollution with different thresholds. Conclusion This study provides a comprehensive picture of the interactions between extreme temperature events and PM 2.5 pollution on total and cause-specific mortalities. The projected interactions call for coordinated policies and public health actions to face the twin challenges, especially the co-appearance of hot extremes and PM pollution.