Chemical characteristics of atmospheric fallout in the south of Xi'an during the dust episodes of 2001-2012 (NW China)

Atmospheric fallouts (AFs) were collected in the south of Xi'an, NW China, during the dust episodes of 2001 -2012. The chemical characteristics of total 68 AF samples including their chemical compositions, size distribution and magnetic susceptibility were studied. The contamination degree and the source of heavy metals in AF were also explored with enrichment factor method and multivariate statistical analysis. The results showed that the particle mass size distribution of AFs dominated by coarse particles (PM10-50) in dust days. The concentrations of 26 elements associated with AFs determined by wavelength dispersive Xray fluorescence spectrometry (WDXRF) in studied sites varied from 92.90 to 188.10 mg kg Cr, 31.40 and 63.00 mg kg(-1) for Cu, 16.60 to 167.30 for Pb and 106.60 to 196.80 for Zn. Their average concentrations found in this study were 139.22 +/- 29.41 mg kg(-1), 46.93 +/- 10.56 mg kg(-1), 78.42 +/- 46.52 mg kg(-1) and 150.61 +/- 32.84 mg kg(-1), respectively, which exceeded their corresponding recommended background values more than two times. While, other elements, such as Br varied from 1.10 to 5.90 with 3.34 +/- 1.60 mg kg(-1) mean, Cs from 2.90 to 10.90 with mean of 7.23 +/- 2.47 mg kg(-1), Ga between 6.90 and 20.80 with 15.23 +/- 3.59 mg kg(-1), Rb in the range of 62.10-124.20 with the average of 80.69 +/- 16.89 mg kg(-1), Y from 9.90 to 35.00 with 20.43 +/- 6.27 mg kg(-1) average, La from 29.60 to 54.20 with mean of 37.28 +/- 8.28 mg kg(-1) and V with average of 81.97 +/- 8.93 mg kg(-1) in the 57.7-92.10 mg kg(-1). Multivariate statistical analysis (principal component analysis and clustering analysis) was suggested that the principal element elements, Al, Fe, Si, K, Ca, Na, Mg, coupled with the trace elements Co, V, Ce, Mn, Ni, Ga, Y, Rb, La, Br, Cs were predominated by crustal material sources, whereas, Cr, Cu, Ba, Sr, As, Pb and Zn were highly influenced by anthropogenic activities. Simultaneously, the water-soluble ions (WS-ions) of NH4+ SO42-, SO32 -, NO3- SiO44-, HSO4- contained in APs identified by FT-IR spectroscopy were possible originated from coal combustion. The results were also confirmed and consistent with the observations of magnetic susceptibility (MS), enrichment factor (EFs) and contamination evaluation analysis. With such rates of atmospheric fallouts that contain elevated levels of toxic elements during the dust storm condition, actions should be taken to continually examine and understand of the potential impacts of AFs on surface ecosystem, water resource, and human health in the dust storm condition. (C) 2013 Elsevier Ltd. All rights reserved.