Heterogeneous Risks of Chemical Components and Sources in Size-Resolved Particulate Matter on Ischemic and Hemorrhagic Stroke.

Atmospheric particulate matter (PM) from different emission sources exhibits distinct size distributions and chemical compositions, which may differentially influence stroke risk. However, how particle size, chemical composition, and emission source jointly shape subtype-specific stroke risks remains unclear. In this study, 58,763 ischemic stroke (IS) and 2,588 hemorrhagic stroke (HS) hospitalizations were analyzed alongside 41 PM chemical components and 6 major emission sources identified across 9 aerodynamic size fractions below 10 μm. Associations between PM physicochemical properties and stroke were assessed in a time-series framework. Stroke risks exhibited pronounced heterogeneity across particle size, chemical composition, emission source, stroke subtype, and demographic groups. IS was associated with a broad range of components below 1.1 μm and above 3.3 μm, whereas HS showed stronger links to specific metals (As, Cu, Fe, Mn, Ni, Pb) and polycyclic aromatic hydrocarbons. Coal combustion (RR per IQR = 1.05; 95% CI: 1.01-1.10) and industrial emissions (RR per IQR = 1.18; 95% CI: 1.00-1.41) were the principal contributors to IS and HS, respectively. Individuals younger than 60 years showed increased HS risks related to most components in size <0.43 μm and industrial emissions. Females showed stronger susceptibility to Cu, traffic-related sources, and resuspended dust. Overall, our findings show that stroke risk varies according to particle size, chemical composition, and emission sources, with distinct patterns across stroke subtypes and population groups. This integrative understanding helps clarify the priority drivers of stroke risk and supports more strategically targeted air quality interventions.