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 (PM2.5 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 PM2.5 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.