Research at the University of Pennsylvania

This dissertation examines the environmental behavior, chemical leaching, and urban transport pathways of tire and road wear particles (TRWPs) with a focus on Philadelphia, a densely built city whose drinking water supply and stormwater infrastructure make it uniquely vulnerable to non-point source pollution. Although TRWPs are often treated as inert physical particles, their complex polymer–filler composition and associated additives allow them to interact dynamically with urban surfaces, stormwater chemistry, and receiving waters. This work approaches TRWPs as both particles and chemical sources, integrating laboratory experiments, field sampling, and particle-scale characterization to better understand their fate in urban environments.

Three complementary research components structure the dissertation:

1. Stormwater Sampling and Urban Loading
   Stormwater was collected during multiple rain events to characterize the concentration, composition, and physical properties of TRWPs mobilized from city surfaces. This chapter documents how rainfall intensity, roadway context, and antecedent dry periods influence TRWP transport. Results highlight the role of combined sewer overflows (CSOs), roadway drainage features, and traffic density in determining urban export of TRWPs.
2. Leaching Experiments and Chemical Release
   Controlled leaching experiments trace the release of organic and inorganic constituents from TRWPs under environmentally relevant conditions. Using LC-MS/MS and ICP-OES, the study quantifies leachate concentrations of compounds such as benzothiazoles, PAHs, and key metals. Results show that leaching is influenced by particle size, composition, and contact time, emphasizing that TRWPs act as active chemical sources rather than inert solids.
3. Particle Isolation, Density Characterization, and Microscale Analysis
   TRWPs were isolated from heterogeneous road dust using density separation and sieving (150 μm cutoff). Microscale and bulk techniques, including SEM, XRD, and image-based measurements, were used to characterize particle morphology, mineral components, and density categories across sites. These analyses reveal how mineral adhesions, filler content, and weathering processes alter particle density and transport potential.

Together, these chapters present an integrated assessment of TRWPs in an urban watershed. The findings demonstrate that TRWPs contribute both physical particles and mobile chemical species to stormwater systems, with implications for water quality, ecosystem health, and urban infrastructure management. By focusing on Philadelphia, a city with aging storm-sewer systems and high reliance on riverine drinking water sources, this dissertation fills a critical geographic and scientific gap in TRWP research. The combined stormwater, leaching, and particle analyses provide a framework for evaluating TRWP behavior in other cities and for informing mitigation strategies aimed at reducing pollutant loads from roadways.