Effect of treadwear grade on the generation of tire PM emissions in laboratory and real-world driving conditions

Tires generally wear out due to the friction between the tire and the road surface. Minimizing tire wear could reduce the non-exhaust particulate matter (PM) emissions from tires. Typically, tire treadwear grade can be used as an indicator of PM emissions from tires. Tires that wear out quickly will produce higher PM emissions than more durable tires. In this study, the effect of treadwear grade on the generation of tire PM emissions was investigated through laboratory and on-road driving measurements. In the laboratory measurements, a tire wear simulator installed in an enclosed chamber was used to eliminate artifacts caused by interfering particles during the generation and measurement of tire wear particles. For realistic on-road driving measurements, a mobile sampling vehicle was employed to sample road dust. The road dust was chemically analyzed using pyrolysis gas chromatography-mass spectrometry (GC-MS) to characterize the tire-road wear particles. Both measurements showed that the higher treadwear grade generated lower tire PM emissions due to the high strength of the rubber, except for the UTQG 700 tire. The UTQG 700 tire, which had the highest treadwear grade, produced higher PM emissions than the UTQG 350 and 500 tires because it readily formed the fine particles due to lamellar peeling rather than tearing or curling of tire treads. Notably, tire nanoparticles were observed in laboratory measurements due to the volatilization and nucleation of the sulphur (S) and zinc (Zn) compounds in the tire tread due to the frictional heat between the tire and paved road surface.