Environmental Geochemical Characteristics Of Chengdu, Near-surface Atmospheric Dust

The thesis focuses on the dust that is 1.5m from the ground. To compare with the usual dustfall, the dust in the thesis is named as air dust near the ground. The content concentrates on the physical characteristics and the spatial distributional characteristics of the air dust near the ground in Chengdu.Conclusions are as follows:Based on the electron microscope scanning on the air dust, the beads, single mineral and polymer are observed; the biggest granula is of 40um,most granulae are within 10um. Through XRD analysis on the single particles, main minerals of the air dust are quartz, felspar, dolomite, calcite, gypsum and barite.The content of the elements or their oxides of Pb, Cu, Cr, Hg, As, Se, Cd, Zn, Mn, V, Ni, S, P, Co, Ti, Fe, Al, Si, K, Mg, Na and Ca in the dust is analyzed. The outcome shows that the contents of Zn, Cu, Pb, Hg, Cd, Cr, Mn and Ni are higher and change greatly except Hg. Of all the elements, the'average contents and the content-range of Pb, Hg, Cd, As and Cr are 374.51ug/g and 119.76-1327.42ug/g, 0.54ug/g and 0.15-2.62ug/g, 4.40ug/g and 0.17-20.80ug/g, 42.43ug/g and 15.31 - 178.80ug/g, 113.88ug/g and 18.99 - 647.08ug/g separately. However, the contents of the oxides change little. The average content of SiO2 is 34.91% and the highest. The counterparts of Na2O, K2O, MgO are the lowest, 1.36%, 1.47%, 1.75% separately. Those of Al2O3, Fe2O3, CaO are 9.41%, 7.44%,8.97% separately. The content-range of SiO2 ,Na2O, K2O, MgO, AI2O3, Fe2O3, CaO are 25.94-50.81 %, 0.94-2.81%, 1.21-3.28%, 0.05-4.21%, 5-16.72%, 3.84-12.44%,5.46-16.05% in turn.The content of Cd in the downtown is very heavy, especially most of the area within the second-circle, and shows sheet distribution; that of Hg and Cd in the downtown is higher, but the areas of the very heavy content of Hg scatter in dot in the reaearch area, that of Pb scatter in dot and centalize nearby the third circle. The content of As is higher in the area around of the third circle and out-circle of south-east in Chengdu, its content in most of the area varies from 30 to 40ug/g, the highest locates the east of Chengdu in dot.Speculating on the source of the elements in the dust, the ashes of coal, the dust of soil, rubbish, metallurgy, traffic are the main sources.