Occurrence and Drivers of Tire and Road Wear Particles in Road-to-Indoor Environments across Urban China

Tire and road wear particles (TRWPs) are a major source of microplastics, while knowledge of their occurrence on a large geographical scale and in the indoor environment is scarce. We performed the first nationwide survey of TRWPs in road-to-indoor environments across 31 cities in China. Paired samples were collected in five compartments and quantified for TRWP concentrations using bonded sulfur as a marker. TRWPs were detected in all samples from road environments and in indoor dust with a detection frequency of 89.7%. The TRWP concentrations were 7.19–148.32 mg/g (road dust), 1.08–29.83 mg/g (roadside soil), 2.82–30.66 mg/g (entrance dust), not detected (ND)–38.51 mg/g (exterior windowsill dust), and ND–15.39 mg/g (indoor dust), with the highest levels in Liupanshui (industrial zone) and megacity Hong Kong. An evident spatial gradient emerged, with East China exhibiting considerably higher TRWP levels relative to the other regions. Regression tree analysis identified the traffic congestion index as the dominant driver governing TRWP abundance, while redundancy analysis further revealed that the gross domestic product and truck proportion were the primary factors influencing TRWP distribution (p < 0.05). This study provides new insights into the nationwide distributions and environmental and anthropogenic drivers of TRWPs in urban environments.