Association of compound exposure to heat wave and ozone pollution with cause-specific cardiopulmonary mortality: A space-time-stratified case-crossover study.

Heat wave and ozone (O) pollution events are increasingly co-occurring in the context of climate change, especially in China. However, the effects of compound exposure to both hazards on cause-specific cardiopulmonary mortality remain largely unclear. In this study, we conducted a space-time-stratified case-crossover study of 550,634 township-level cardiopulmonary deaths in Anhui Province, China, from 2013 to 2021 to systematically evaluate the associations of exposure to heat wave and O pollution with multi-cause cardiopulmonary mortality and quantify their interactive effects Under various definitions, the odds ratios (ORs) of cardiopulmonary mortality associated with heat wave-only events, O pollution-only events, and compound events exposure ranged from 1.15 (95 % CI: 1.14-1.16) to 1.39 (95 % CI: 1.37-1.41), 1.02 (95 % CI: 1.01-1.03) to 1.04 (95 % CI: 1.03-1.04), and 1.22 (95 % CI: 1.20-1.23) to 1.75 (95 % CI: 1.62-1.88), respectively. Notably, more significant synergistic effects of heat wave and O pollution exposure at lag 1 day were observed on mortality risk from hypertensive heart disease, ischemic heart disease, acute myocardial infarction, hemorrhagic stroke, and chronic obstructive pulmonary disease. Females, older adults, and residents living in rural-dominated mixed regions experienced higher compound exposures. During the study period, the estimated number of excess cardiopulmonary deaths attributable to compound events exposure under various definitions ranged from 243 (95 % CI: 201-285) to 3227 (95 % CI: 2974-3480). More than 90 % of these excess deaths occurred after 2017 and were primarily concentrated in densely populated northern and central-eastern townships. These findings underscore that coordinated governance of air pollution and climate change could maximize reductions in the cardiopulmonary mortality burden.