An EXAFS Study on the Local Structure Around Iron in Atmospheric Aerosols Collected in the Qingdao Area

Jianhua Qi,Zhihu Sun,Zhi Xie,Tiandou Hu,Xianguo Li,Lijuan Feng,Manping Zhang

doi:10.3390/80100031

Jianhua Qi, Zhihu Sun + Show 5 more

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The existing forms of Fe are of great interest since they have a profound effect on the biological availability of Fe. In this work, aerosol samples collected in different seasons and at different locations in the Qingdao region were examined by means of extended X-ray absorption fine structure (EXAFS) K-edge analysis of Fe, X-ray diffraction (XRD) and Fe content analysis. The results showed that an iron ion in aerosol particles is surrounded on average by 5.8 (coordinated) O ions. For the six samples examined, the coordination number of the first Fe-O coordination subshell is always 3 with a coordination distance (with O) in the range of 1.952~1.966±0.002 Å, while the coordination number of the second subshell varies from 2.2 to 3.0 with a coordination distance of 2.108±0.002 Å. The coordination is approximately consistent with that of α-Fe2O3, suggesting that iron in aerosol samples is mainly present in the form of α-Fe2O3. The fact that the coordination number in the second subshell is smaller than that of α-Fe2O3 might be an indication that there is a small amount of FeO mixed with α-Fe2O3 in aerosol particles. Existence of FeO is confirmed by a later XRD experiment.

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Atmospheric aerosols are particles and/or droplets suspended in air [1]
The characteristics and variation of the local iron structures for aerosol samples collected in different seasons and at different sites in the Qingdao area were examined by means of Fe K-edge extended X-ray absorption fine structure (EXAFS) analysis
Where k is the photoelectron wave number and Si(k) is a dimensionless functio n of k assigned to the attenuation of the EXAFS signal due to multiple excitation effects; Fj (k), Φj, σj, λ(k) are the jth atoms′ backscattering amplitude function, energy dependent phase shift in the photoelectron wave, Debye-Walker factor and the photoe lectron mean free path respectively; Rj, Nj are the mean internuclear distance between the central atom and the atoms of the jth neighbour shell and the coordination number of the jth shell respectively

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Introduction

Atmospheric aerosols are particles and/or droplets suspended in air [1]. They play very important roles in atmospheric processes [2], environmental quality [3], and the biogeochemical cycles of trace elements and compounds [4], even though they contribute very little to the atmospheric constituents of the earth.Trace metal elements loaded in aerosol particles are of great interest since they have profound effects on the geochemical cycle of metals and on the marine ecosystem. It is very difficult for conventional X-ray diffraction (XRD) method to detect the local structures of iron in aerosol particles because of its low content. The characteristics and variation of the local iron structures for aerosol samples collected in different seasons (spring and summer) and at different sites in the Qingdao area were examined by means of Fe K-edge EXAFS analysis.

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