Temperature modulation of adverse consequences of ozone exposure on cardiovascular mortality: A study of multiple cities in China

Worldwide epidemiological studies indicate that the adverse health effects associated with ozone exposure might be modified by ambient temperature. In China, the health risks associated with ozone exposure are poorly understood due to the lack of data. In addition, it is insufficient how temperature modifies the ozone exposure-cardiovascular mortality association. In this study, we adopted two advanced time-series Poisson generalized additive models (GAMs) including a nonparametric bivariate response surface model and a stratification parametric model to investigate the modification effect of temperature on ozone-related cardiovascular mortality in 13 cities in China from 2014 to 2016. We categorized temperature into three levels (low, moderate, and high) considering four temperature percentiles, including the 25th and 75th, 15th and 85th, 10th and 90th, and 5th and 95th temperature percentiles. Subsequently, under different temperature stratifications, we evaluated acute cardiovascular mortality risks associated with the maximum 8-h average ozone concentration (O3-8hmax) in each city and assessed these O3-8hmax-cardiovascular mortality associations by meta-analysis in all cities together. The results confirmed that high temperature strongly increased the O3-8hmax cardiovascular mortality association; in particular, the O3-8hmax mortality risk was highest when the 95th temperature percentile cut-off was applied. On days with daily mean temperatures exceeding the city-specific 75th, 85th, 90th, and 95th percentiles, a 10-μg/m3 increase in the O3-8hmax during the current and previous day (lag01) increased the cardiovascular mortality risk by 0.74%, 0.76%, 0.80%, and 1.11%, respectively. However, the O3-8hmax mortality risk did not change appreciably under moderate or cold temperature conditions defined by different temperature cut-offs. Our findings validate the theory that high temperature increases health risks associated with the O3-8hmax; thus, mitigating ozone exposure will be of utmost importance, especially under the context of a changing climate.