Quantifying tire wear particle dynamics: insights from a hydrological-based material flow analysis in urban watersheds

Abstract Tire wear particles (TWPs) constitute a significant fraction of total microplastic release, necessitating quantification for effective management. While material flow analysis (MFA) quantifies their pathways from generation to environmental sinks, existing approaches apply uniform transfer coefficients across entire regions, obscuring critical spatial heterogeneity essential for assessing ecosystem exposure. This study developed a spatially explicit, process-based MFA framework by integrating mechanistic TWP generation modeling with hydrological rainfall-runoff processes to quantify TWP generation, road surface accumulation, and storm-driven mobilization in Hong Kong. Results indicate an annual per capita TWP generation of 0.28 kg/person/year, notably lower than the global average. Over half of the generated TWPs were mobilized by stormwater runoff after road surface deposition. The hydrological transport pathway to surface water exhibits pronounced spatial and event-driven heterogeneity. Spatially, while suburban districts with extensive road networks dominated absolute emissions (24%), dense urban cores exhibited generation intensities 15 times higher and washoff intensities 18 times greater than outlying low-density areas. In terms of event dynamics, storm-event modeling demonstrates that extreme precipitation following prolonged dry periods can mobilize 30% of annual TWP loads within 24 h, fundamentally reorganizing pollution distributions. This framework provides a transferable tool for pinpointing TWP hotspots and informing targeted mitigation strategies in urban watersheds worldwide.