Types and concentrations of tire wear particles (TWPs) in road dust generated in slow lanes

Drivers commonly navigate their vehicles at moderate speeds in proximity to traffic lights. In this study, road dust samples were collected in the vicinity of traffic lights, as well as at a taxi stand (TS) situated between traffic lights, with considerations given to both forward direction (FD) and backward direction (BD). The characterization of tire wear particles (TWPs) in the road dust was meticulously conducted based on particle size. Notably, tire-road wear particles (TRWPs) were conspicuously absent in samples surpassing 500 μm. Furthermore, TRWPs comprised less than 1% of identified particles in the road dust samples of 212-500 μm, with their origin traceable to heavy vehicles rather than passenger cars. The abundance of TRWPs from heavy vehicles exhibited marked variations, with heightened prevalence in the TS and BD samples as opposed to the FD sample. For the samples smaller than 212 μm, the composition of natural rubber (NR) in TWPs demonstrated a diminishing trend with escalating particle size. Conversely, the composition of styrene-butadiene rubber (SBR) exhibited an upward trajectory independent of the sampling site. The NR composition ratio in TWPs followed the order: TS (17-55%) > FD (17-47%) > BD (13-36%), while the SBR composition ratio exhibited the sequence: BD (62-86%) > FD (48-79%) > TS (24-70%). The TWP concentrations in road dust obtained from the TS (0.35-0.82%) were discernibly lower than those in the FD (0.54-1.77%) and BD (0.61-1.29%) samples. Specifically, the average TWP concentrations in road dust samples, falling within the size range of 20-212 μm, were 0.45%, 1.06%, and 0.91% for the TS, FD, and BD samples, respectively. These concentrations were lower than the corresponding values observed in samples collected from a bus stop.

Comparison of polymeric components and tire wear particle contents in particulate matter collected at bus stop and college campus

Particulate matter (PM_2.5) samples were collected at two different places of a college campus (CC) and a bus stop (BS) nearby the college campus. The traffic volume of college campus was very low due to untact classes. Polymeric components and tire wear particle (TWP) contents in the PM_2.5 samples were analyzed using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Various polymeric components such as natural rubber (NR), bitumen, saturated hydrocarbons, poly(ethylene terephthalate) (PET), and plant-related particles (PRPs) were observed. NR and bitumen are key components of TWP of bus tire tread and asphalt pavement wear particle (APWP), respectively. The TWP contents in the PM_2.5 samples collected at the bus stop were larger than those collected at the college campus. For the same sampling site, the TWP content in the PM_2.5 sample collected for higher fine dust concentration in the air was greater than that for lower one. The TWP_2.5 concentration in the air for the BS sampling was higher than those for the CC sampling, even when the PM_2.5 concentration in the air for the former was lower than those for the latter. It can be concluded that the TWPs and APWPs in the PM_2.5 samples collected at the college campus should be transferred mostly from the outside road.

Analysis of Polymeric Components in Particulate Matter Using Pyrolysis-Gas Chromatography/Mass Spectrometry

Particulate matters (PMs) such as PM10 and PM2.5 were collected at a bus stop and were analyzed using pyrolysis-gas chromatography/mass spectrometry to identify organic polymeric materials in them. The major pyrolysis products of the PM samples were isoprene, toluene, styrene, dipentene, and 1-alkenes. The pyrolysis products generated from the PM samples were identified using reference polymeric samples such as common rubbers (natural rubber, butadiene rubber, and styrene-butadiene rubber), common plastics (polyethylene, polypropylene, polystyrene, and poly(ethylene terephthalate)), plant-related components (bark, wood, and leaf), and bitumen. The major sources of the principal polymeric materials in the PM samples were found to be the abrasion of the tire tread and asphalt pavement, plant-related components, and lint from polyester fabric. The particles produced by the abrasion of the tire tread and asphalt pavement on the road were non-exhaustive sources, while the plant-related components and lint from polyester fabric were inflowed from the outside.