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

Abstract

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. 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 revealed a nonlinear relationship, with CVD mortality risk peaking at an O₃ concentration of 229.7 µg/m^³ (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. 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.