Chemical Composition of Urban Street Sediments and Its Sources

The distribution and the concentrations of various chemical elements in street sediments were investigated along a rural urban boundary in Beijing, China. The statistical factor analysis of the data concerned identifies two anthropogenic sources responsible for the contamination of Beijing air. The first source is a steel factory in the western part of Beijing. From this source, Mn, Fe and Ti were emitted into the atmosphere through chimneys and by wind from coal heaps used as the primary energy source for the factory. The second source is a combination of traffic, domestic heating and some small factories in the center of Beijing urban area discharging Cu, Pb, Zn and Sn. Grain size analyses show that most of the metals in the road dust have higher concentrations in the small grain size fraction <0.125 mm, which is the severest case because these small particles with larger specific surface area and high heavy metal contents fly up easily and float in the air for a long time. Besides the anthropogenic contamination, such elements as Y, Zr, Nb, Ce and Rb are derived mainly both from natural soils and from the deserts. This is supported by mineral phase analysis, which shows a clear imprint of materials in road dusts coming from the west China deserts. Our results clearly show that the chemical compositions of the urban road dusts can be used to identify distinctive sources responsible for the contamination mentioned above. The study shows that the chemistry of road dusts is an important monitor to assess the contamination in the urban environment