Water Quality Drives PAHs Fate in Urban Stormwater Runoff: The Pivotal Role of DOM Composition and Evolution

The evolution of dissolved organic matter (DOM) in urban stormwater runoff drives the migration and transformation of polycyclic aromatic hydrocarbons (PAHs). The sources of DOM and PAHs in stormwater runoff are complex, and research on the driving mechanisms behind their migration and transformation remains insufficient. In this study, the optical properties of DOM and the spatial source distribution of PAHs in urban stormwater runoff were systematically analyzed. The abundance of DOM components varied significantly across different urban functional zones, with DOM exhibiting a mixed characteristic of both autochthonous and allochthonous sources (FI = 1.4–1.9), while the contribution of local sources was limited (BIX < 1). PAHs concentrations were highest in traffic and vegetation-covered areas, primarily originating from traffic emissions. Total phosphorus (TP), chemical oxygen demand (COD), and pH were identified as the main driving factors for DOM components, with rainfall increasing the proportion of humic-like components in rivers. Furthermore, PAHs showed significant correlations with pH and COD. Finally, TP, pH, and fluorescence properties had a notable influence on the characteristics of the C3 and C4 components, while humic-like components (C1 + C2) directly and positively affected PAHs. This study provides theoretical support for the prevention and control of stormwater runoff pollution.