Tire, Road or Both - Examining the Sources of Ultrafines at the Tire-Road Interface
Siriel Saladin, Josh Hassim, Molly J. Haugen, David O'Loughlin, Chiara Giorio, ADAM M BOIES, University of Cambridge
Abstract Number: 625
Working Group: Chemicals of Emerging Concern in Indoor and Outdoor Aerosol: Sources, Vectors, Reactivity, and Impacts
Abstract
Tire–road interactions generate airborne and settled nanoparticles that contribute to urban particulate pollution and can enter waterways. However, the mechanisms, sources, and chemical signatures of tire-derived nanoparticles remain poorly characterized. Here, we simulate tire wear using a rotating-drum abrasion system at Karlsruhe Institute of Technology under tracer-gas–controlled drive cycles and collect the resulting nanoparticles for detailed analysis.
We quantified particle-number emission indices during standardized cycles and applied complementary online (size-resolved chemical ionization) and offline (ICP-MS, high-resolution mass spectrometry) methods to characterize particle composition. Drive-cycle trials showed that roughly 70 % of emitted nanoparticles are semi-volatile species, likely formed by thermal vaporization of tire polymer binders at the contact interface. ICP-MS confirmed the presence of tire-specific trace elements (e.g., Zn, S, Mg) in the ultrafine fraction, although distinguishing tire versus pavement contributions remains challenging.
To improve source apportionment, we developed sampling protocols capable of collecting tens of micrograms of nanoparticles for elemental and molecular analyses and are evaluating stable-carbon isotope ratios to differentiate elastomer-derived carbon from asphalt and concrete substrates. Complementary Soxhlet extraction of cryomilled tire material with polar solvents revealed a 10–15 % mass loss of oligomeric and cyclic hydrocarbon binders. Thermal aging of air-dried tire particulates in a tube furnace (20–250 °C) produced substantially fewer nanoparticles than untreated samples, implicating volatilized binders as primary emission precursors. Ongoing tests across diverse roadway materials aim to quantify pavement-specific effects on nanoparticle chemistry and establish robust emission factors.
These findings advance our mechanistic understanding of tire wear nanoparticle formation and composition, laying the groundwork for improved source-apportionment studies and targeted mitigation strategies for non-exhaust traffic emissions.