Characterization of airborne tire particle emissions under realistic conditions on the chassis dynamometer, on the test track, and on the road

Tires have already been identified as a major source of microplastics and airborne particles, and with the increasing use of alternative powertrains and heavier vehicles, the importance of tire and road wear particles (TRWP) is growing. As part of this comprehensive study, a new sampling system was developed to measure the particle number concentration (PNC) of TRWP emissions from 4 nm to 10 µm. Airborne emissions were characterized on the chassis dynamometer using an aerosol fast sizer, which revealed a bimodal size distribution with a dominant ultrafine emission mode at approximately 10 nm and a larger mode at 270 nm. Investigation of the collected particles using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) provided insight into two different formation mechanisms for ultrafine particles including evaporation and condensation. The emission indices of four driving cycles (WLTC Class 3, LA4, US06, and Großglockner) were determined on the chassis dynamometer and compared with a real driving emission test. The influence of road surface and lateral acceleration on the amount of TRWP and their size distribution was investigated by mobile measurements on the test track and on the real road. Both the choice of test cycle and the test environment have a significant influence on detected tire emissions: The number of particles emitted per kilometer differs strongly between the driving cycles, while the test environment and cornering have an influence on the particle size distribution.