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The soils from residential areas of Xi'an city were selected as a case area. The absolute principal component scores-multivariate linear regression (APCS-MLR) model and the ordinary kriging interpolation were combined to identify and apportion the pollution sources of soil heavy metals (As, Ba, Co, Cu, Mn, Ni, Pb, Sr, Zn,V), the percentage of contribution of every source for every element, and the spatial distribution characteristics of contribution rates. Compared with the background values of cinnamon, which is the main soil type in Xi 'an, the accumulation levels of Pb, Cu, Sr, Co, Zn, Ba, Ni, As, Mn, V in soil of urban residential areas in Xi'an city decreased in turn. The standard-exceeding ratios of Ba, Co, Cu, Pb, Sr, Zn were higher than those of other studied elements. Three main pollution sources of soil heavy metals in residential areas were natural source, traffic sources, and fossil fuel combustion source, respectively. Natural source was the main source of As, Mn, Ni, V in studied residential areas. The average contribution rate of natural source for As, Mn, Ni, V was 69.63%, 74.28%, 68.65%, 77.09%, respectively. The fossil fuel combustion was the second largest contributor for their accumulation in these studied residential areas. Its contribution rate for As, Mn, Ni was 23.07%, 19.09%, 23.13%, respectively. The contribution of traffic emissions was lower. Their spatial distribution characteristics tended to be lower in west and higher in east. The average contribution rates of fossil fuel combustion source for Co, Pb, Sr, Zn were 59.84%, 42.22%, 44.50%, 44.44%, respectively. The performance of spatial distribution was increased gradually from the city center to the outside. The sources of Ba were given priority to natural source and fossil fuel combustion source, and the average contribution rates were 41.67% and 48.27%, respectively. The contribution rate of fossil fuel combustion source for Ba gradually decreased from the center of the city. The contribution rates of natural source, traffic source, and fossil fuel combustion source for Cu were 37.00%, 20.47% and 26.50%, respectively.

The magnetic susceptibility and the concentrations of Co, Cr, Cu, Pb, Sn, Sr and Ba in topsoil samples from Xi'an City were measured to study their spatial distribution and their correlation in this study. The results show that the concentrations of all measured heavy metals are higher than their background values in Cinnamon topsoil, which is the main soil type of Xi'an City. The heavy metals concentrations and the magnetic susceptibility of the studied samples display moderate variance. Co, Cr, Cu, Pb, Sn, Sr and Ba are significantly positively correlated with low-frequency magnetic susceptibility, while are significantly negatively correlated with frequency susceptibility. The spatial distribution of low-frequency magnetic susceptibility is identical with the concentrations of Pb and Cu. However, the spatial variation of frequency magnetic susceptibility is different from the concentrations of Co, Cr and Ba. The pollution assessment results show that the heavy metal pollution in topsoil of Xi'an City is moderate. The spatial contribution of the pollution load index was significantly correlated with the magnetic susceptibility of topsoil in Xi'an City. Therefore, soil magnetic susceptibility can be used as an effective monitoring means for heavy metal pollution in urban soil.