Mass flow analysis of tire-wear particles, including carbon black, and implications for road dust management

Representative non-exhaust emissions from automobiles and tire-wear particles (TWPs) accumulate in road dust, causing their dispersion into the surrounding environment. TWPs undergo fragmentation due to continuous abrasion and weathering, resulting in the release of carbon black (CB), a major component of tire rubber. Although previous studies have conducted mass flow analyses (MFAs) for TWPs based on vehicle and road types, a detailed MFA specifically addressing road dust, including CB-bound TWPs, has not been performed. In this study, annual emissions of TWPs, including CB, from road dust were estimated based on different vehicle and road types. Mass flow diagrams were constructed to illustrate the distribution of these particles across technical and environmental compartments for each road type. The environmental mass of TWPs, including CB, in each compartment was calculated based on sewage system type, runoff ratio, road cleaning efficacy, and UV exposure. The MFA results indicate that highways contribute significantly to TWP exposure in soil and air, despite a substantial portion of TWPs also accumulating as road residue. Additionally, the endpoint mass flow of the environmental media (4241 t/a to air, 3140 t/a to water bodies, 20,602 t/a to soil, 3044 t/a to landfill, and 12,712 t/a to road residue) and the predicted environmental concentration values (1.16 μg/m³ in air, 0.37 mg/L in water, and 1824 mg/kg in soil) were consistent with literature ranges, supporting the reliability of the findings. These results underscore the importance of targeted road dust management strategies to mitigate the environmental impact of non-exhaust emissions.