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.

Automated summary

This study proposes a method for quantifying the concentration of total and free-bound carbon black (CB) in road dust using a combination of four analytical tools. The results show that road dust from closed sites has significantly higher tire-wear particle (TWP) and free-bound CB content compared to open sites. Additionally, unintentional driver respiratory exposure to PM fixed in vehicle filters was discovered.