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

Abstract

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 a-Fe2O3, suggesting that iron in aerosol samples is mainly present in the form of a-Fe2O3. The fact that the coordination number in the second subshell is smaller than that of a-Fe2O3 might be an indication that there is a small amount of FeO mixed with a-Fe2O3 in aerosol particles. Existence of FeO is confirmed by a later XRD experiment.

Keywords

• Atmospheric aerosol
• EXAFS
• iron speciation
• Qingdao