Chemical composition and sources of PM_2.5 and TSP collected at Qinghai Lake during summertime

PM_2.5 and total suspended particulate (TSP) samples were collected from June to September 2010 at Qinghai Lake, northeastern Tibetan Plateau. The concentrations of major water-soluble ions, 10 elements, elemental carbons (ECs) and organic carbons (OCs) were quantified. Mass concentrations of PM_2.5 and TSP were 21.27±10.70μgm^-3 and 41.47±20.25μgm^-3, respectively, and the mean ratio of PM_2.5/TSP was 0.51. The greatest anion and cation in both PM_2.5 and TSP samples were SO₄^2- and Ca²⁺, respectively. Crustal elements, such as Ca, Fe and K, were the main elements in our aerosol samples, and their enrichment factors (EFs) were lower than 10. EFs for Pb, As, and Zn were greater than 10, indicating that they were influenced by anthropogenic sources. EC concentrations were 0.33±0.17μgm^-3 and 0.47±0.28μgm^-3, whereas OC concentrations were 1.49±0.63μgm^-3 and 2.30±0.95μgm^-3 in PM_2.5 and TSP, respectively. Based on the calculated ratios of EC/TC and K⁺/EC, most of the ECs were found to be related to biomass burning emissions. Because of the pollution from local sources, the ratios of OC/EC were 4.77±1.32 and 5.23±1.39 in PM_2.5 and TSP, respectively, which were lower than those of other remote sites. Salt particles produced by the salty lake reacted with acid gases and caused most of the nitrates and a small fraction of sulfate to be distributed in coarse mode; Cl deficit was also observed in our aerosol samples. Results of backward trajectories and correlation analysis show that the concentrations of SO₄^2-, OCs, As, Pb, and Zn, were influenced by the long-distance transport from eastern China.