Pilot analysis of tire tread characteristics and associated tire-wear particles in vehicles produced across distinct time periods

Owing to stringent vehicle emission regulations and the shifting automotive landscape towards clean-energy vehicles, the emission of non-exhaust tire-wear particles and its implications for microplastic contamination have garnered substantial attention, emerging as a focal point of research interest. Unlike traditional source apportionment methods involving direct environmental sampling, this study focuses on the physical and chemical attributes of tire treads, the tread temperature changes, and the tire-wear particle emissions of three light-duty vehicles manufactured between 2011 and 2021. This study advances the understanding of the effects of tire properties on particle emissions, which provides preliminary information on low-wear tires. The results show that tire-wear particle emissions, mainly composed of ultrafine particles in terms of number, heavily depend on the elevated tread temperatures. The change in tread temperature is influenced not only by the initial tread temperature but also by tread pyrolysis characteristics. Ca, Mg, and Zn are abundantly contained in the tire tread and tire-wear particles.

Rapid estimation of tire-wear particle concentration in road dust using PM10 and traffic data in a ternary plot

Air pollution, a pressing global issue, is significantly exacerbated by airborne particulate matter (PM), affecting air quality and human health. Urban vehicular activities majorly contribute to PM rise through both exhaust and non-exhaust emissions. Despite strides in managing exhaust emissions, non-exhaust particles, such as tire wear particles (TWP) remain under-addressed. This research proposes a method for estimating TWP concentrations using PM10 data and traffic activity, which could offer a valuable tool for controlling roadside fine particles and TWP. This paper introduces a ternary plotting technique and step-by-step procedure to estimate TWP levels in road dust using only PM10 and traffic data. Traditional analysis of TWP via pyrolysis-gas chromatography-mass spectrometry is complex and time-consuming. Hence, our proposed approach presents an alternate method that leverages readily accessible PM and traffic data, providing critical information for road management interpretation. The triangular plot analysis demonstrated a linear correlation: [log(Traffic) + 2]-[250,000/TWP-13]-0.18PM10. While the resulting correlation may vary based on specific road conditions, the method can be tailored to different regions, offering insights into efficient estimation of TWP concentrations and promoting improved roadside pollution management.

Estimation of microplastic emission and transfer into Tokyo Bay, Japan, using material flow analysis

To reduce microplastic (MP) discharge into the aquatic environment, it is necessary to properly identify its sources and amounts. Here, specific MP sources, i.e., personal care products (PCPs), fibers from clothes, and tire-wear particles (TWPs) were focused, and MP generations from these sources in the Tokyo Bay watershed, Japan, were estimated based on statistical data on production and reported emission factors of the MP sources and executing considering uncertainty on the data. Potential annual MP emission into Tokyo Bay was estimated to be 10.2 ± 1.6, 38 ± 22, and 1500-1800 tons for PCPs, fibers, and TWPs, respectively. Emissions into Tokyo Bay by assuming MP density and diameter was estimated. For fiber, the fraction to potential emission was estimated at 1.0-2.8 %. This study contributes to determining potential discharge pathways. This will assist in the application of appropriate measures to reduce MP discharge into water bodies.

Quantitative analysis of the concentration of nano‑carbon black originating from tire-wear particles in the road dust

Exhaust and non-exhaust particulate matter (PM) is regarded as the most significant airborne during driving. Among the source of non-exhaust PM, the tire-wear particles (TWP) can be quantified using pyrolysis-gas chromatography/mass spectrometry (Py-GC-MS). TWPs are fragmented by continuous weathering once exposed to the road. Approximately 5 wt% of carbon black (CB) bound in the rubber matrix of TWPs tends to detach from it, and thus some portion of free-bound CB could be co-existed in the road dust. Although there are existing methods for analyzing pure CB and TWPs, only few analysis techniques on the amount of free-bound CB in contaminant samples have been discovered. Herein, we propose a method for quantifying the total and free-bound CB in road dust using a combination of four analytical tools: a semi-continuous carbon analyzer, element analyzer, thermogravimetric analyzer, and Py-GC-MS. This study is the first attempt in quantifying the concentration of nano-CB derived from TWPs in road dust. The proposed methodology was applied to the samples collected from five open sites, three closed sites, and four types of air conditioner (AC) filters in passenger vehicles. Compared to the samples obtained in open sites, the road dust in the closed sites exhibited 21.5 times higher TWP content (59,747 mg/kg) and 5.1 times higher free-bound CB content (14,632 mg/kg). In addition, unintentional driver respiratory exposure to PM fixed in the vehicle filters was discovered owing to the increase in CB and TWP contents in aged AC filters.