Integrated Risks from Air Pollution and Climate Extremes: Synergistic Effects of Ozone, Heat, and Humidity on Cardiovascular Mortality

Background Climate change has significantly increased adverse effects on cardiovascular disease(CVD). Ozone (O ₃ ) exposure is recognized as a risk factor for CVD mortality. However, few studies have analysed the modifying effects of climatic factors on O ₃ , particularly in subtropical regions. This study analyzed the association between O ₃ 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 a Distributed Lag Nonlinear Models (DLNMs) to assess lagged and cumulative O ₃ effects. For the modification effect, a general linear model (GLM) was used to quantify the extra effect of temperature and relative humidity on O ₃ -related CVD mortality risks. A series of sensitivity analyses were conducted to assess the robustness of the effect modification by temperature-humidity interactions on O ₃ -associated cardiovascular mortality. Results Results revealed a nonlinear relationship, with CVD mortality risk peaking at an O ₃ concentration of 229.7 µg/m³ (Odds Ratio, OR = 1.330, 95% Confidence interval, CI: 1.110-1.600) and a delayed maximum effect at 6.2-day lag. High temperature (T > P ₉₅ ) and moderate humidity (40% ≤ RH < 70%) amplified O ₃ -associated mortality ( β = 0.160, P < 0.001). Sensitivity analyses demonstrated robustness across alternative climate thresholds and COVID-19 adjustments. Conclusions O ₃ 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.