Determination of heavy metal content in dust of earth's surface and dust on air conditioner filter by X-ray fluorescence analysis

Abstract

The dust of earth's surface and the dust on air conditioner filters reflect a certain area of air pollution in a period of time. In the present study, we investigate the dust collected from the Wangjiang campus of Sichuan University on March, 2017. The dust is divided into 9 groups according to their diameters. The dust is made into the samples by mixing the dust and analytically pure starch at a ratio of 1:2, and pressing it into slices of 1.5 cm in radius and 6 mm in thickness through using a powder compressor. Likewise, the salts (MnSO4H2O, Fe(NO3)39H2O, CuSO45H2O, ZnSO47H2O, Pb(NO3)2), are also made into standard samples of different elements (Mn, Fe, Cu, Zn, and Pb). X-ray fluorescence analyzer is used to measure the element content in each of the samples according to calibration curves measured from the standard samples. The results show that the content of each element in the earth's surface dust is lower than that in the dust on the air conditioner filter. The values of Cu, Zn, and Pb content in the dust are higher than the average content of the topsoil in Sichuan Province, China. These elements possibly originate from motor vehicle exhaust. Based on the theoretical model for the gaseous elements to change into the fine particulate matter, the change of the trace element content with the particle size can be expressed as Ci kiDn, where Ci is the content of the metal element i in the dust, ki is a scale factor, D is the diameter of the dust particle, and n is the distribution index. From the results it is concluded that the distribution indexes corresponding to various elements are approximately the same in the size range of interest to us (32.5-230 m). A recommended value of n is -0.430.06.