Spatial and temporal distribution of platinum group elements (PGEs) in roadside soils from Shanghai and Urumqi, China

The aims of this study are to elucidate the temporal trend, spatial distribution and the source of platinum group elements(PGEs) in roadside soil from Shanghai and Urumqi. The roadside surface soils from different types of road were collected in both Shanghai and Urumqi. The spatial and temporal distributions of PGEs in roadside soils were determined by ICP-MS. The average annual PGE concentrations from different types of roads in Shanghai occurred in the following order: highway > urban road, suggesting that total PGE concentrations were associated with driving speed. However, no significant difference in the concentrations of PGEs from different roads in Urumqi indicated that other factors also affected PGE distribution, such as driving conditions and traffic density. The temporal trends of PGEs were different between Shanghai and Urumqi. Levels of PGEs were low in spring and summer and high in autumn and winter in Shanghai. However, the trend was reverse in Urumqi because of the different forms of precipitation (rain vs. snow) and the occurrence of dry weather conditions in that city. Additionally, the highest concentration of Pt (23.5 ng g(-1)) was observed in winter in Urumqi, suggesting that coal combustion may be another important source of Pt in northern Chinese cities. This study suggests that the spatiotemporal distribution of PGEs in soils is affected by the age of the catalytic converter used, traffic density, the type of catalytic converter used, and weather conditions. Although the PGEs were usually thought to be mainly from the abrasion and deterioration of catalytic converters, the coal combustion is also an important potential source of Pt, especially northern cities where coal combustion is high in winter.