Atmospheric wet deposition of trace elements to central Tibetan Plateau

To investigate trace elements in wet precipitation over the Tibetan Plateau (TP), a total of 79 event-based precipitation samples were collected from September 2007 to September 2008 at Nam Co Station. Samples were analyzed for concentrations of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb using inductively coupled plasma-mass spectrometry (ICP-MS). The annual volume-weighted concentrations of elements were generally comparable to other background sites, and much lower than urban areas. The enrichment factors (EF) showed that, in comparison with the Tibetan soils, the wet precipitation had elevated concentrations of Cr, Co, Ni, Cu, Zn, Cd and Pb, probably indicating their anthropogenic origins. Other elements (Al, Fe, Mn and V) with enrichment factor value of <10 may derive mainly from crustal sources. The principal component analysis further confirmed the two different groups of elements in wet deposition samples. The backward trajectories were calculated for each precipitation event using the NOAA HYSPLIT model. The results indicated significant differences of EF for trace elements of anthropogenic origin between the summer monsoon and non-monsoon seasons. The data obtained in the present study indicated that pollutants can affect remote high altitude regions like the Tibetan Plateau through long-range transport, especially in the summer monsoon season.