To study the characteristics of bulk and surface elemental composition of ambient PM2.5 in 5 Chinese cities, which are differently affected by sand-dust events.
Between 16 April and 17 May, 2008, ambient PM2.5 were sampled in sand-dust source terrains (Hotan city) and in sandstorm-affected zones (Korla, Dunhuang, Lanzhou, and Beijing). X-ray photoelectron spectroscopy and x-ray fluorescence were used to analyze surface elemental composition, chemical states, and total elemental composition of PM2.5, respectively. The elemental data were also processed using factor analysis to identify their sources.
The surface and bulk elemental composition of ambient PM2.5 among different cities varied significantly. In Beijing and Lanzhou, the percentages of surface elements (carbon-containing compounds, nitrogen-containing compounds, and sulfate), as well as bulk elements (zinc, sulfur, copper, and lead), were much higher than those in the other 3 cities. In Hotan and Korla city, the surface and bulk element contents (sodium, iron, calcium, potassium, chlorine, silicon, aluminum, and magnesium) of PM2.5 were significantly higher than those in Beijing and Lanzhou; zinc, iron, and magnesium were found to be enriched on the surface of PM2.5. Following are the results of factor analysis:
- Bulk and surface elements such as sodium, iron, calcium, potassium, chlorine, silicon, aluminum, and magnesium came from natural sources, whereas zinc and sulfate came from anthropogenic sources;
- Surface elements including aliphatic carbon, carbon combined with nitrogen, carbonyl carbon, organic nitrogen, and ammonium salt were anthropogenic pollutants;
- Of bulk elements, manganese came from natural sources, whereas copper and lead came from anthropogenic pollutants.
In the areas that were seriously affected by sandstorm, the bulk and surface elemental composition of PM2.5 had greater proportion of natural sources, whereas in the areas less affected by sandstorm, the elemental compositions had greater proportion of anthropogenic sources.