Heavy Metal Partitioning to Particles in Snow Exposed to Urban Traffic - Distribution across the Particle Gradation

摘要

Compared to rainfall runoff, snow has a much longer residence time in the urban environment.rnIn addition snow has a porous matrix making it an effective medium for accumulation ofrnanthropogenic constituents generated by urban activities such as traffic. Traffic activitiesrngenerate a wide gradation of anthropogenic solids in part through tire-pavement abrasion. Thesernparticulate solids accumulate in snow exposed to traffic and urban activities and remain asrnresidual deposition material after the melting and recession of the snow from the urban surface.rnThis study analyzed the physical characteristics of these residuals and the distribution of heavyrnmetals partitioned to these residuals for 10 urban highway sites located throughout metropolitanrnCincinnati. Results from the residuals analyses indicate that for all sites particle gradationsrnranged from almost 10,000-μm to less than 25-μm with a mean d50 of 1225-μm. Specific gravityrn(ρsg) of residual solids ranged from 2.5 to 3.2 as evaluated for all discrete intervals across therngradations, with the lower specific gravity associated with particles less than 100-μm. For eachrngradation, specific surface area (SSA) generally increased with decreasing particle size while thernpredominance of total surface area (SA) was associated with the coarser size fractions.rnCumulative analysis for Pb, Cu, Cd and Zn associated with snow residuals indicated that morernthan 50% of the heavy metal mass was associated with residual material greater than 250-μm andrngenerally more than 80% was associated with particles greater than 50-μm. Pearson correlationrncoefficients suggested a very strong relationship between cumulative heavy metal mass andrnresidual cumulative total surface area as well as residual cumulative particulate mass. Resultsrnprovide guidance for development of management, control and treatment of urban snow andrnresiduals associated with urban snow.