Magnetic Studies Of Street Dust And Topsoil Along Traffic Artery In Shanghai

Urban street dust pollution is one of environmental concerns. Shanghai, the largest city with dense population and developed industry in China, is facing serious street dust pollution. According to the successful practices of Environmental Magnetism in street dust pollution, this paper conducted magnetic properties, particle size measurements and geochemical analysis of street dust and near topsoil in the traffic arteries across the city center to the outskirt of Shanghai, so as to explore the role of Eenvironmental Magnetism in street dust pollution monitoring in Shanghai. The results are as follows:The street dust magnetic susceptibility(χlf) ranges from 34.61×10-8m3kg-1 to 1035.82×10-8m3kg-1 with a mean value of 530.11×10-8m3kg-1. Topsoil(χlf) ranges from 27.00×10-8m3kg-1 to 328.33×10-8m3kg-1 with a mean value of 69.19×10-8m3kg-1. Compared with topsoil, dustχlf is significantly enhanced, which indicates higher content of magnetic minerals and serious pollution in street dust. Spatially, magnetic susceptibility is higher in dusts collected from urban center areas than those in the suburban areas. It decreases from inner ring to outer ring, but magnetic susceptibility is very high in Baoshang District. Industry and transportation are main factors influencing magnetic susceptibility in the study area.There is a strong linear correlationship betweenχlf and saturation isothermal remanent magnetization(SIRM) in dust and topsoil, which indicates ferrimagnetic minerals dominate the magnetic properties of the samples. Hysteresis loop and thermal magnetic analysis sugest that ferrimagnetic minerals are primarily composed of magnetite. Magnetic particles are mainly multi-domain(MD) and pseudo single domain(PSD) in size, which are coarser in dust than in topsoil. SEM analysis identifies spherical particles as well as irregular particles in both dust and topsoil, which indicates input of magnetic particles derived coal combustion.Particle size analysis indicates that dust samples are coarser, showing multi-peaks in the distribution curves, which indicates the source of dust is more diverse and complex.Enrichment factor analysis shows that dust is significantly polluted by Pb, Zn, Cu and Cr, whose mean contents are 100.83 ppm,428.47 ppm,164.04 ppm and 109.22 ppm, respectively. Topsoil samples showes a lesser degree of polution. Pollution Load Index(PLI) reveals that most dust samples are subjected to heavy metals pollution.Correlation analysis reveals that there are significantly positive correlation betweenχlf, SIRM,χARM, HIRM and the above-mentioned elements and PLI, which show that the above-mentioned magnetic parameters can be used to indicate heavy metal pollution of dust in Shanghai.