Identification of Long-Range Transport Pathways and Potential Sources of PM10 in Tibetan Plateau Uplift Area: Case Study of Xining, China in 2014

Abstract

ABSTRACTThe aim of the study is to identify long-range transport pathways that may have an important influence on PM10 levels in plateau uplift area, namely Xining in northwestern China. Cluster analysis was applied to identify the main trajectory groups in horizontal direction and 3D cluster analysis was employed to identify the origins and distributions of major trajectory groups in vertical direction. Potential Source Contribution Function (PSCF) and Concentration-weighted Trajectory (CWT) were applied to identify the major potential source areas (PSA). Based on the temporal and spatial distribution of backward trajectories, four major trajectory pathways were clustered. The results indicated that Xining was easily affected by inland trajectories in four seasons but there were obvious results that different trajectories have dissimilar influences on the mean PM10 concentrations. In horizontal direction, the long-range transport pathways were obvious in spring and winter while a few of long-range transport pathways could be found in summer and autumn. Because wind mainly came from north or west in spring and winter and it was very strong, which had a big influence on the transportation of transport pathways while wind in summer and autumn had a small impact on the transportation of transport pathways. In vertical direction, in the 700 hPa barometric altitude (3000 m) above, air masses in winter and spring with long transport pathways were the most important back-trajectories which had a great influence on Xining city. In summer and autumn, Xining was mainly influenced by airflow distributed below 700 hPa barometric altitude. In spring and winter, eastern Xinjiang, border areas between Gansu and Inner Mongolia and southern Tibet in China with the highest Weight Potential Source Contribution Function (WPSCF) and Weight Concentration-weighted Trajectory (WCWT) values were the dominant potential sources, which demonstrated the contribution from sources outside of Xining were significant. In summer and autumn, WPSCF values outside of Xining were no more than 0.5 (most of them were less than 0.3) and WCWT values were almost lower than 100 µg m–3 in those two seasons, which suggested that there were no main important PSA in those two seasons. Furthermore, the study also revealed that Tibet in China was one of the potential sources of PM10 in Xining.