Integrated risks from air pollution and climate extremes: synergistic effects of ozone, heat, and humidity on cardiovascular mortality

Abstract

Background: Climate change has significantly increased adverse effects on cardiovascular disease (CVD). Ozone (O3) exposure is recognized as a risk factor for CVD mortality. However, few studies have analyzed the modifying effects of climatic factors on O3, particularly in subtropical regions. This study analyzed the association between O3 and CVD mortality in Zhejiang Province, China, while evaluating the modifying effects of temperature and humidity. Methods: Using mortality, air pollution, and meteorological data from 11 cities (2019–2023) in Zhejiang Province, China, we employed distributed lag nonlinear models (DLNMs) to assess lagged and cumulative O3 effects. For effect modification, a general linear model (GLM) was used to quantify the extra effect of temperature and relative humidity on O3-related CVD mortality risks. A series of sensitivity analyses were conducted to assess the robustness of the effect modification by temperature–humidity interactions on O3-associated cardiovascular mortality. Results: Results revealed a nonlinear relationship, with CVD mortality risk peaking at an O3 concentration of 229.7 µg/m³ (relative risk (RR) = 1.330, 95% confidence interval (CI): 1.110–1.600) and a delayed maximum effect at a 6.2-day lag. High temperature (T > P95) and moderate humidity (40%≤ RH < 70%) amplified O3-associated mortality (β = 0.160, P< 0.001). Sensitivity analyses demonstrated robustness across alternative climate thresholds and COVID-19 adjustments. Conclusions: O3 exposure significantly increases cardiovascular mortality, with risks amplified by high temperature and moderate humidity. These findings highlight the necessity of integrating climate interactions into region-specific air quality policies and public health warnings.