Magnetic properties of street dust and topsoil in Beijing and its environmental implications

摘要

Environmental magnetic measurements were carried out on the samples of street dust and topsoil, which were collected along the roadway in the urban and suburb of Beijing, including magnetic susceptibility (chi), anhysteretic remanent magnetization (ARM), isothermal remanent magnetization (IRM) of all samples and temperature-dependence of magnetic susceptibilities and magnetic hysteresis parameters of representative samples. Obvious differences exist between the samples of street dust and those of topsoil. Compared with topsoil samples, the concentration of magnetic particles and high-coercivity components in street dust samples are higher, and the magnetic grains are coarser. Both dust and topsoil samples are dominated by ferrimagnetic minerals, and iron particles are only detected in some dust samples. These results suggest that street dust samples reflect the characteristic of particles produced by industrial and traffic activities, and the magnetic property of topsoil samples represents the characteristic of particles from both anthropogenic and natural sources. The distribution of magnetic parameters is influenced by the environment where the samples are collected, like industry, traffic density and other road conditions. Hard isothermal remanent magnetization (HIRM) may be used as an indicator of particles produced by traffic activity. Dust storm samples collected on 17 and 18 April, 2006 have different magnetic properties from street dust and natural particles, like loess and paleosol, which indicate that the dust storm might be mixed with anthropogenic particulates during transport and falling.