Spectroscopic analysis of iron-oxide minerals in aerosol particles from northern China

Diffuse reflectance spectrometry was used to study iron-oxide minerals and to investigate the reflectance characteristics of eolian dust collected during the spring of 2001 and 2002 on bulk filters from three sites in northern China. The first derivatives of the reflectance spectra were consistent with signals from two iron-oxide minerals, hematite and goethite, at wavelengths of 565 and 435 nm, respectively, and these values varied with the iron concentrations in the samples. The percent reflectances for the yellow, orange and red bands increased with the iron concentrations and with the first derivative values representing hematite and goethite while those for violet, blue and green bands decreased correspondingly. The results show that iron-oxide minerals play an important role in determining the aerosol particles' color and reflectance properties. Moreover, the relative amounts of the two iron-oxides in Asian dust apparently differ from those in African dust, suggesting that the iron-oxides may provide another tool for tracing the origins of eolian dust on a global scale.