探讨富集因子背景值的选择

为探讨富集因子(EF)背景值的选择,利用黑龙江省甘南县大气降尘重金属元素数据,分别选用黑龙江省A层土壤环境、平均大陆地壳、大陆上地壳为背景,计算Cr、Mn、Ni、Pb、As、Cu、Zn的EF值.研究表明,采用平均大陆地壳和大陆上地壳元素丰度作为背景值时,Pb、Zn、As等元素的EF均值大于2,元素富集一定程度上与人为输入作用有关;采用黑龙江省A层土壤作为背景,As元素EF均值小于2,元素在大气中的富集主要为自然输入;通过相关性分析,As与Cr、Mn、Ni、Cu同为自然源,结果与选用黑龙江省A层土壤为背景时判别结果较一致.本文认为,导致不同背景值取得的EF值差异较大的原因为自然条件下元素的富集和亏损,采用区域土壤元素背景值能够较为准确地判断大气降尘中元素的主要来源.

Selection of the background value for enrichment factor

To make an appropriate choice of the Enrichment Factor(EF) background values,dustfall in Gannan,Heilongjiang province,was chosen to calculate the EF values of Cr,Mn,Ni,Pb,As,Cu and Zn with references of the A-layer soil in Heilongjiang Province,the average continental crust and the upper continental crust,respectively.When the average continental crust and the upper continental crust are chosen as backgrounds,the average EF values of Pb,Zn and As are all greater than 2.It is suggested that the anthropogenic input should be partly responsible for the enrichment of these elements.Nevertheless,the average EF value of As is less than 2 when the A-layer soil in Heilongjiang Province is referenced,implying that natural input mainly contributes to the enrichment of As.The result of correlation analysis shows that both As and Cr,Mn,Ni,Cu are naturally sourced,which is consistent with the result that referenced with the A-layer soil in Heilongjiang province.Thus,it can be concluded that the difference of EF values with varied references is likely to be caused by the enrichment or depletion of the specified elements in natural environment.Regional soil is more suitable to be referenced in determining the major sources of elements in dustfall.