Speciation of elements in atmospheric particulate Matter by XANES

Study on the elemental speciation in atmospheric particulate matter is important for control of pollution and evaluation of toxicity. X-ray absorption fine structure (XAFS) spectroscopy is a powerful technique to investigate chemical speciation. It is a non-destructive technique, keeping the original speciation in the samples, so reliable information can be obtained. The experiments are performed with synchrotron radiation. The high intensity and other advantages of synchrotron radiation significantly improve the precision of experiments. The XAFS in which the energy region is near absorption edge is called X-ray absorption near edge structure (XANES), it provides information of electronic structure of absorption atoms, so can reflect oxidation state and chemical speciation of elements. In the present work, the atmospheric particulate matter samples with different particle size and different sampling site were collected in Shanghai, China. The XANES spectra of Cr, Mn, Cu and Zn were measured. The XANES spectroscopy was used as a fingerprint to compare with those of reference materials to obtain speciation information. The oxidation state of these elements and main chemical components in the samples were described using the method. The results show that in our samples oxidation state of Cr is tervalence, the main components are chromite and chromic oxide. Mn mainly exists as divalence, the main components are sulfate and other compounds of divalence Mn. Cu also exists as divalence, the main components are hydrated copper sulfate and copper oxide. Zn mainly exists as zinc sulfate. For the XANES spectra of samples with different particle size and different sampling site, we did not find their obvious differences. It means they have similar speciation. In addition, the elemental concentrations in the samples were determined by proton induced X-ray emission (PIXE) technique. The difference of elemental concentrations was observed in the samples with different sampling site and different particle size.