Evidence for extender oils in thermally generated tyre nanoparticles.

Tyre-derived nanoparticles are an increasingly acknowledged component of road traffic emissions due to their potential health impacts. Although nanoparticle formation from tyres has frequently been attributed to evaporation-condensation processes, the chemical identity of the vapour-phase precursors remains unknown. In this work, we combined controlled thermal generation, solvent extraction, and nuclear magnetic resonance (NMR) spectroscopy to investigate thermally generated tyre nanoparticles. Cryomilled passenger car tyre tread was heated in a tube furnace, isolating thermal effects in the absence of mechanical abrasion. A clear onset of nanoparticle formation was observed above approximately 110 °C to 130 °C. Extracting the tyre tread with chloroform reduced cumulative nanoparticle emissions at 200 °C by 99% and 70% for two different tyre samples, indicating that nanoparticle formation at this temperature is dominated by solvent-accessible tyre constituents rather than the cross-linked rubber matrix. 1H and 13C NMR spectra of the generated nanoparticles were dominated by aliphatic hydrocarbon signals inconsistent with rubber polymer-derived molecules. Instead, the spectra matched the composition of common tyre extender oils, an essential component of passenger car tyre tread present at mass fractions on the order of 20%. Our results indicate that thermally generated tyre nanoparticles in the pre-pyrolysis regime originate predominantly from mobile, solvent-accessible hydrocarbon species consistent with extender oils. These findings provide a basis for risk assessments and toxicological evaluations of tyre wear nanoparticles, although microscopic temperatures at the tyre-road interface remain unknown and may extend beyond commonly assumed ranges.