Chemical characterization and temperature dependence of volatile submicron tire wear particles formed by evaporation–condensation

Tire wear particles can form via two distinct pathways—mechanical abrasion and evaporation–condensation—resulting in aerosol particles with different size ranges and chemical signatures. This study investigates the volatile submicron fraction produced via evaporation–condensation by generating seed-coated aerosols from seven tire materials in a tube furnace and characterizing them using a soot-particle aerosol mass spectrometer (SP-AMS) coupled with SMPS measurements. Across all tires, particle growth onsets occurred at Tgo ≈ 144–163 °C and new particle formation associated with high-temperature “smoldering” at Tso ≈ 178–200 °C, with systematic differences between passenger-car and heavy-duty tires. The composition of the volatilized tire-derived aerosol particles was dominated by hydrocarbon fragment ions (e.g., m/z 41, 43, 55, 57, 69) with a distinct aromatic contribution at m/z 91 (C7​H7+), and the particles also contained oxygenated fragments at m/z 60 and 73 that are commonly attributed to biomass burning, highlighting potential source–attribution ambiguity in urban environments. Comparison with mechanically generated tire dust showed enrichment of unsaturated and higher-mass hydrocarbon fragments in the non-volatilized material, consistent with lower volatility. These results provide reference SP-AMS signatures and temperature-dependent indicators for volatile tire-derived submicron aerosol and support interpretation of laboratory and ambient measurements of tire wear emissions.