Mortality risks associated with ozone exposure: Modified by temperature and mediating temperature effects

Short-term exposure to ozone has been linked to increased mortality, but its role in temperature-health associations is still not fully understood. Beyond direct effects, ozone may influence mortality as both a factor modified by temperature and a mediator of temperature's impact. We conducted a time-series study using quasi-Poisson generalized additive models (GAMs) to examine associations between short-term ozone exposure and cause-specific mortality in Hefei, China (2014-2022). To assess whether temperature modified the ozone-mortality relationship, we estimated ozone effects across low, moderate, and high temperature strata. We also performed mediation analysis to evaluate whether ozone served as an intermediate factor linking temperature to mortality. Subgroup analyses were conducted by sex, age, and education. Ozone exposure was positively associated with non-accidental, cardiovascular, and cerebrovascular mortality. These effects were stronger under lower temperature conditions. Compared with moderate temperatures, low temperatures significantly elevated the ozone-related risks for non-accidental mortality (P = 0.04), and cerebrovascular diseases (P = 0.01). Mediation analysis showed that ozone explained 25.21 % of temperature-related all-cause mortality and up to 38.33 % for cardiovascular mortality. Older adults, females, and individuals with lower education levels showed higher vulnerability. Ozone contributes to mortality both directly and indirectly by mediating temperature effects. Addressing this dual pathway through stronger year-round ozone control and by incorporating temperature-ozone interactions into health warning systems may help reduce risks, particularly among vulnerable groups.