Temperature Modification of Ambient Ozone Association with Outpatient Visits for Atherosclerotic Cardiovascular Diseases

Scarce evidence exists on the impact of ozone (O3) on atherosclerotic cardiovascular disease (ASCVD) morbidity in tropical urban settings, and whether temperature modifies this effect remains unclear. To bridge this gap, we assessed the association between ambient O3 and ASCVD outpatient visits, and the potential effect modification by temperature, in Haikou, China. A time-series analysis was performed on data from 163,348 daily hospital outpatient visits for ASCVD collected between 1 January 2020 and 31 December 2022. The association between O3 exposure and daily visits was evaluated with an over-dispersed Poisson generalized additive model (GAM), and the modifying effect of temperature was scrutinized using a nonparametric bivariate response surface model. A 10 μg/m3 increment in the daily maximum 8 h average concentration of O3 was associated with a 1.35% (95% CI: 0.63, 2.07) increase in ASCVD outpatient visits at lag0. Stratified analyses revealed that the association between O3 and ASCVD visits was only significant during the warm season, with stronger effects observed above 30 °C, peaking at 34 °C (lag06). The combined exposure to high temperature and O3 concentrations significantly amplified ASCVD outpatient visits. Ambient O3 exposure was associated with increased ASCVD outpatient visits in the tropical city, and this risk was enhanced under high temperatures. These results highlighted the importance of considering temperature interaction in O3-related risk assessments.