Magnetic Characteristics and Environmental Pollution Analysis of Street Dust in Different Functional Zones of Xi'an City

Abstract

Urban environmental pollution can be revealed by the magnetic characteristics of street dust. Environmental magnetic measurements were carried out for the 151 samples of street dust collected in different functional zones of Xi'an city. Magnetic susceptibility varied within the range between 169.5×10-8 m3·kg-1 and 977.48×10-8 m3·kg-1, and the χlf average value was 415.66×10-8 m3·kg-1,which was 10 times higher than that of the background value. Isothermal remanent magnetization varied within the range between 2005.31×10-5 A·m2·kg-1 and 10897.64×10-5 A·m2·kg-1, and the SIRM average value was 5105.99×10-5 A·m2·kg-1. The average value of frequency-dependent magnetic susceptibility was 1.30, which was extremely low. The SIRM curve was consistent with χlf curve. The results indicated a high concentration of magnetic minerals in street dust. The magnetic minerals were mainly low-coercivity ferrimagnetic (magnetite and maghemite) and anti-ferromagnetic minerals (hematite), which contributed to the magnetic susceptibility. The main domains of magnetic minerals were composed of multiple domain (MD) and pseudo-single domain (PSD) ferrimagnetic minerals demonstrating the pollution of environment. According to the spatial distribution of magnetic properties of street dust and the different functional zones of Xi'an city, seven districts (A, B, C, D, E, F and G areas) were divided, which were summarized as three pollution types:heavily polluted, moderately polluted and lightly polluted. In the ecological district of Baqiao (F area) which was heavily polluted, χlf, SIRM and soft values were all the highest in the seven areas, and the main pollution sources were industry and vehicle emission. χlf, SIRM and soft values were slightly higher in the high-tech industrial district (A area) and the central business and commerce district (B area), which was moderately polluted by industry and vehicle emission. However, the magnetic parameters were relatively low in the functional zones of education, tourism and culture (C, D, E and G area), demonstrating that these areas were only slightly polluted by vehicle emission.