An X-ray photoelectron spectroscopy study of elements on the surface of aerosol particles

Total suspended particulate (TSP) samples were collected at three sites, before and during a major dust storm in March, 2002. For comparison, PM10 (particulate matter with aerodynamic diameters less than ) were collected at one of the three sites. X-ray photoelectron spectroscopy (XPS) was employed to analyze the surface composition and iron species on aerosol particles. Results were compared with bulk analysis using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). It was shown that aluminium and cadmium were present as Al2O3 and CdO on particle surfaces. The majority of lead was in the form of PbSO4, while carbonate or oxide was the major species of zinc. Sulfate was the main compound of sulfur. It was found that surface iron species were the most complex ones. The curve fitting of Fe 2p peaks showed that the main existing forms of surface iron were oxide, sulfate, silicate and phosphate, with some compounds adhering to SiO2 and/or Al2O3 particles. The surface atomic ratio of Fe to Al on aerosol particles had a good correlation with its bulk ratio. The surface ratio of S to Al in pre-storm samples were higher than in storm ones, suggesting that sulfur was substantially enriched on particle surface during non-dust period. It is speculated that surface S plays a role in reducing surface Fe (III) to Fe (II).