Occurrence, Emission, and Transport of Tire and Road Wear Particles across Four Environmental Compartments along Ring Road Networks in Beijing

Tire and road wear particles (TRWPs) are an appreciable source of microplastics (MPs); however, knowledge of their large-scale occurrence and mass flux based on robust sampling and quantification is limited. Herein, the first city-wide survey of TRWPs across environmental compartments (road dust, snowbank, water, and sediment from rivers and lakes) along four ring roads (beltways) in Beijing was performed. TRWP concentrations (n = 74) were quantified using bonded-sulfur as a marker to reveal the city-wide spatial distributions and adopted to establish a framework estimating TRWP emission factors (EFs) and mass flux from generation to remote atmospheric, terrestrial, and aquatic transport. The TRWP concentrations were 0.46 × 10⁴–3.55 × 10⁴ μg/g (road dust), 0.65–46.18 mg/L (water), 0.28 × 10⁴–1.79 × 10⁴ μg/g (sediment), and 9.46–19.12 mg/L (snowbank) and were highly related to nearby traffic conditions. Based on total EFs (34.4–288.5 mg/vKT) and airborne EFs (6.2–17.2 mg/vKT) calculated from the preceding concentrations, the TRWP emissions in Beijing were determined as 1.28 × 10⁴ t/a. Among them, 61.3% was eventually disposed of in landfills owing to frequent road sweeping and high runoff treatment efficiency and 18.1% was stranded on the roadside; nevertheless, 11.9% escaped to freshwater systems and 5.7 and 3.0% airborne transported to remote land and ocean, respectively. This study provides new insights into the emissions and fate of TRWPs.