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Three-dimensional distribution of roadside airborne/tire-wear particles and implications for pedestrian exposure
Summary
Tiny bits of tire and road dust—including microplastic particles—float highest right near the ground, meaning kids and pets are exposed to more of this pollution than adults since they breathe closer to the road surface. The study found these particles drop off quickly as you move away from traffic and get less concentrated higher up, suggesting that dry sweeping/vacuuming roadside dust (rather than hosing it down, which just washes it into waterways) could be a practical way to cut down on what pedestrians breathe in.
Non-exhaust traffic particles in roadside air are chemically complex and spatially heterogeneous; however, exposure assessments often rely on limited near-ground measurements. We examined the three-dimensional distributions of resuspension-driven airborne particles, including tire-wear particles (TWP), carbonaceous particles (e.g., carbon black (CB) aggregates), and metals using distance-resolved surface dust (Zone A; 0-30 m), height-resolved airborne sampling within the pedestrian layer (Zone B; 0-2 m), and foliar deposition as a time-integrated sink (Zone C), combined with a rainfall wash-off evaluation. Surface dust and TWP showed strong distance-dependent decline, while CB exhibited weaker distance dependence. Filter-based airborne particles decreased sharply with height (703.8-34.6 µg/m from 0 to 2 m), with particulate matter showing mid-height peaks around 0.5-1 m, indicating size-dependent stratification from vehicle-induced turbulence. Leaf deposition decreased with height (deposited area 99% lower at 2 m than at 0 m), and the magnetic Fe-oxide fraction in leaf-deposited material (27.9-17.3%) exceeded that of bulk road dust (6.7-7.1%), suggesting selective metal-rich particulate interception. A 3D concentration field was derived by coupling distance-dependent surface reservoirs with height attenuation using Amato-type loading dependence (exponent 0.81), predicting near-road hotspots and breathing height variability. Heavy rainfall suppressed the off-road reservoir while shifting contaminants toward runoff. These findings suggest that physical removal of deposited roadside dust may help reduce the resuspendable reservoir while avoiding runoff transfer associated with water-based cleaning; however, the short-term airborne effects of vacuum-assisted cleaning were not directly evaluated in this study.