Characteristics of Tire Wear Particles Generated by a Tire Simulator under Various Driving Conditions

Physicochemical properties of pure tire wear particles (TWPs) were investigated in a laboratory. A tire simulator installed in an enclosing chamber was employed to eliminate artifacts caused by interfering particles during the generation and measurement of TWPs. TWP particulate matter (PM_2.5 and PM₁₀) was correlated with tire speed ( r > 0.94) and load ( r > 0.99). Their mass size distributions showed that TWP mode diameters ranged between 3 and 4 μm (unimodal). Tire wear caused by slip events resulted in an increase in the number concentration (ca. 8.4 × 10⁵ cm^-3) of particles (mainly ultrafine particles (UFPs)) at low PM_2.5 and PM₁₀ values (1 and 2 μg m^-3, respectively). During braking events, UFPs were emitted at an early stage, with an increase in number concentration (up to 1.1 × 10⁷ cm^-3); a high mass concentration (3.6 mg m^-3) was observed at a later stage via the coagulation of early emitted UFPs and condensation. On the basis of morphology and elemental composition, TWPs generally had elongated (micrometer-scale) and round/irregular (submicrometer-scale) shapes and they were classified into C/Si-rich, heavy metal-containing, S-containing, and mineral-containing particles. This study determined that TWP emissions can vary with changes in driving condition.