Association between Low-Concentration PM2.5 Exposure and Emergency Department Visits for Cardiovascular Diseases: A Time-Series Study

Zhang Jiadong¹Ying Wang¹Zhao Li²Jichao Peng³Lifeng Dai⁴Nan Li¹Yang Yi¹Xiaoran Liu^1*

• ¹The First Affiliated Hospital of Hainan Medical University, Haikou, China
• ²Haikou People's Hospital, Haikou, China
• ³Hainan Medical University International School of Public Health and One Health, Haikou, China
• ⁴Southeast University, Nanjing, China

Substantial epidemiological evidence suggests that both short- and long-term exposure to fine particulate matter (PM₂.₅; aerodynamic diameter ≤ 2.5 μm) increases cardiovascular disease (CVD) risk. However, uncertainty persists regarding the cardiovascular effects of low-level PM₂.₅ exposure. This study aimed to clarify the association between PM₂.₅ and CVD morbidity in Haikou, China. A time-series design with DLNMs was employed to assess the short-term associations between PM₂.₅ exposure and daily CVD-related ED visits across three major hospitals in Haikou, with stratified analyses by sex and age. Between 2018 and 2021, 988,020 ED visits were recorded, of which 69,099 (7.0%) were CVD-related. Among CVD cases, 54.09% occurred in patients aged ≥65 years, and 60.04% were male. Cerebrovascular diseases accounted for the largest proportion (46.6%), followed by hypertensive (14.2%) and ischemic heart diseases (14.2%). The temporal distribution of CVD visits displayed clear seasonality, peaking during winter and declining during summer. Our analyses revealed a distinctive three-phase, S-shaped nonlinear association between short-term PM₂.₅ exposure and emergency CVD visits in Haikou, characterized by pronounced lag effects. Specifically, the risk of CVD did not rise monotonically with increasing PM₂.₅ but instead exhibited an initial decline, followed by an increase and subsequent attenuation at higher concentrations. We propose that this complex pattern reflects a balance between adaptive hormetic responses at low exposures, toxic effects at moderate levels, and behavioral adaptations (e.g., reduced outdoor activity) during high pollution episodes. These findings underscore that maintaining PM₂.₅ concentrations within a moderate range may yield greater public health benefits than targeting ultralow levels, offering critical guidance for refining air quality standards and preventive interventions in low-pollution regions.