Size Distribution of Chemical Components of Particulate Matter in Lhasa

To explore the contributions of chemical components in the particulate matter in Lhasa, the size distribution characteristics of the chemical components, such as carbonaceous species (organic carbon, OC; elemental carbon, EC), water-soluble ions (NH4+, Cl-, SO42-, and NO3-) and trace elements (Na, Ca, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, K, Mg, and Pb), were investigated from August 2018 to May 2019. Principal component analysis (PCA) was also used to simulate the source of the particulate matter. The chemical components showed bimodal size distributions, except for Cu. The highest mass concentration of OC appeared at < 0.49 mu m, and the second highest one existed at 1.5-3.0 mu m in winter or at 3.0-7.2 mu m in other seasons. The maximum concentrations of NH4+, Cl-, SO42-, and NO3- were at < 0.49 mu m and peaked at 0.95-1.5 mu m or > 3.0 mu m. For seasonality, the concentrations of NO3- and SO42- were considerably higher in summer and autumn; trace elements (except for Cu, Zn, V, and Ni), OC, and EC presented higher values during late autumn and winter. The ratio between OC and EC (4.15-33.80) indicated the existence of secondary pollution in Lhasa. The [NO3-]-[SO42-] ratios during summer and autumn exceeding 1 suggested that the currently predominant vehicle exhaust made a greater contribution to the aerosols. According to the results of a PCA, the main pollution sources of particulate matter in Lhasa were suspended dust, biomass burning, fossil fuel combustion, secondary pollution, and vehicular emissions.