Association between daily circulatory emergency ambulance dispatches and short-term PM2.5 exposure in a heavily polluted area.

Emergency ambulance dispatches (EAD) have been proven to be associated with ambient particulate matter with diameter < 2.5 μm (PM_2.5) concentration, but the associations of circulatory EAD remained inconclusive, especially in heavily polluted areas. In this time series conducted in Shenyang City, Northeastern China, we explored the associations between circulatory EAD and ambient PM_2.5 and its constituents. Data including 113,508 circulatory EAD records, five types of PM_2.5 constituents, and meteorological information spanning from 2014 to 2019 were retrieved. Using generalized additive models (GAMs), we explored the association between circulatory EAD and calculated excess risks induced by a 10 μg/m³ increase (ERR₁₀) in PM_2.5 mass and its constituents. ERR by percentage change (ERR_pc) to compare among the different constituents were also calculated. Positive associations between circulatory EAD and PM_2.5 mass, sulfates, organic matters, and black carbon, were found particularly at lag0 and lag0-5, with the ERR₁₀ of 3.8% (3.2%-4.4%), 6.5% (2.2%-10.8%), 4.2% (1.7%-6.6%), and 30.2% (17.2%-43.4%) at lag0-5, respectively. Similar associations were observed for cardiovascular EAD, while cerebrovascular EAD suggested a positive association with O₃ rather than PM_2.5 or its constituents. Notably, PM_2.5 mass exhibited the largest ERR_pc for circulatory and cardiovascular EAD, followed by sulfates and black carbon. Moreover, the risks were enhanced for circulatory and cardiovascular EAD in males compared to females and during warmer seasons compared to colder seasons. Our findings contribute new evidence on PM_2.5 exposure and circulatory EAD in relatively polluted areas.