Comparison of traffic-related micro- and nanoplastic concentrations at three urban locations

Abstract

One predominant source of microplastics emitted into the atmosphere is tyre- and road wear particles (TRWPs). Only a handful of studies have quantified atmospheric TRWP concentrations. Our objective was to study variations in TRWPs, compared to other primary traffic pollutants, at locations with different traffic conditions. In 2022–2023, three locations with different traffic-flow and speed (a stop-and-go busy road, highway and urban park), were repeatedly visited for 4-hrs resulting in 23 measurement days. Particles were collected on quartz filters using a high-volume sampler with PM10-inlet and analyzed using double-shot pyrolysis-gas chromatography-mass spectrometry for the mass of synthetic- and natural rubbers (NR). Concentrations of combustion and brake-wear-related traffic air pollutants were measured, including PM10, black carbon (BC), ultrafine particles (UFP) and trace elements. We calculated spatial contrasts and correlations. We observed relatively low levels of sampling- and analysis rubber marker contamination. Synthetic- and NR levels ranged between 2.9 to 42.5 ng/m3 and 1.6 to 26.8 ng/m3, respectively. Compared to the park, rubber markers were 2.8 to 4.6 times higher at the stop-and-go and 2.0 to 2.7 times higher at the highway. These contrasts were larger than for UFP and PM10, but similar to BC and brake-wear related components. Park synthetic rubber levels were modestly higher than field blanks. Rubber markers were highly correlated (r = 0.66 to 0.98) and weakly correlated with most other air pollutants, except for BC and brake wear-related trace elements (r = 0.36 to 0.77). We found substantially increased atmospheric TRWP levels near major roads compared to a park. The measurements from this study will be used for testing associations with health effects.