北京大气降尘中微量元素的空间变异

在北京市六环内均匀布点采集了城市核心区、城市扩展区、近郊区的大气降尘.对降尘中14种稀土元素(Y、Pm除外)以及Cr、Co、Mo、Cd、Pb等5种重金属元素的化学特征进行统计分析,并结合判别分析和Spearman相关分析方法阐释了影响各区域空间变异的主要元素.最后利用三角图解法揭示空间差异的成因.结果表明,各元素含量在空间上具有明显的阶梯变化,Cr、Mo、Cd、Pb含量沿城市核心区向近郊区方向呈递减趋势,Co与14种稀土元素含量的梯度变化特征则恰好相反,由市中心向外围郊区呈递增趋势.轻稀土富集程度表现为城市核心区>城市扩展区>近郊区,Eu亏损程度相反.Mo、Co、Pb元素可用来表征区域降尘的空间差异(68.2%).LaCeSm三角图解表明北京降尘主要来源于壳源物质.PbCoMo和CrCoMo三角图解可以很好地解释不同污染源贡献程度的差别是造成降尘中微量元素在空间尺度上的差异的原因.近郊区降尘受到土壤扬尘、燃煤的影响较大.城市核心区降尘主要受到交通排放的影响.城市扩展区处于过渡带,降尘受到交通、燃煤、土壤扬尘等的影响作用居中.

Spatial variations of airborne dust trace elements in Beijing

Using dust samples collected in urban, suburban area in Beijing during heating period, chemical characteristics of lanthanoid elements (La-Lu) and 5 heavy metals (Cr, Co, Mo, Cd, Pb) were analyzed in order to subsequently discuss the variation in spatial distribution. Discriminant Analysis, together with Spearman Correlation Analysis, was used to identify significant variables influencing the variation. Ternary diagram was further applied to explain the differences. The results demonstrated that the elements had obvious spatial variations along an urban-rural gradient. The concentrations of Cr, Mo, Cd and Pb and the degree of lighter lanthanoids fractionation presented a decreasing trend from urban core to suburb. On the contrary, the amount of Co, lanthanoids abundance and Eu-anomalies increased towards the suburb. Mo, Co and Pb accounted for 68.2% of total spatial variance. The LaCeSm diagram showed that the major origin of airborne dust in Beijing came from crustal materials. The PbCoMo and CrCoMo diagrams sufficiently explained that spatial variations of trace elements were due to the different contributions of pollution sources. The airborne dusts in suburb were mainly derived from soil and chimney soot. While the atmospheric dusts in urban core were primarily influenced by traffic emissions. In the middle transitional zone, the influences of the above sources were medial.