Seasonal variation in characteristics of wear microparticles of high density (> 1.8 g cm−3) produced on road

Wear microparticles are produced on roads by traffic, and they can be transferred to rivers and seas settling as sediments. The sedimentation rate increases with increasing particle density and size. In this study, the types and amounts of high-density wear microparticles (HDWPs, >1.8 g cm^-3) in road dust were investigated. The HDWPs ranging from 106 to 1000 μm were classified into eight categories depending on the color, shape, and physical property: mineral particles (MPs), asphalt pavement wear particles (APWPs), glass particles (GPs), glass beads (GBs), tire-road wear particles (TRWPs), plant-related particles (PRPs), road paint wear particles (RPWPs), and plastic particles (PPs). The HDWPs in road dust were the most abundant in winter (94.0-95.6 wt%), while being the lowest in spring (82.7-90.7 wt%). MPs accounted for over 50 wt% of the HDWPs; however, TRWPs were not found in HDWPs larger than 200 μm. The HDWPs produced by the abrasion of roads, including asphalt pavements and marking paint, exceeded 90 wt%. The non-crosslinked organic components in the HDWPs were removed by chloroform treatment. The chloroform-soluble components in the HDWPs were much more present in winter than in other seasons. Swelling TRWPs with chloroform released mineral particles on the surface.