Atmospheric Aerosol Elements over the Inland Tibetan Plateau: Concentration, Seasonality, and Transport

ABSTRACT

Between November 2005 and November 2007, weekly total suspended particle samples were collected at the Nam Co station in the inland Tibetan Plateau (TP). Through inductively coupled plasma mass spectrometry, twenty-nine elements were analyzed and their sources and fluxes were investigated. Mean elemental concentrations were lower than those at the edge of the TP. Some elements, such as Cr, Ni, Cd, and Pb, exhibited high enrichment factors (Cr: 22; Ni: 17; Cd: 23; and Pb: 9), indicating possible anthropogenic influence in this remote region, particularly during the pre-monsoon and monsoon seasons. In addition, an empirical orthogonal function analysis revealed the dominance of crustal-origin elements, rather than anthropogenic elements, in the aerosol. Furthermore, backward air mass trajectories demonstrated that the Nam Co region was mainly influenced by air masses from Central and South Asia. Accordingly, because of dust storms from Central Asia and within the TP, crustal element concentrations, such as of Al, were higher during winter and pre-monsoon seasons than during the monsoon season. By contrast, anthropogenic elements, such as Cr and Cd, were relatively higher during the pre-monsoon and monsoon seasons because of pollutants transported from South Asia, where atmospheric brown clouds are concentrated and biomass combustion is prevalent. Dry deposition of aerosols dominated in the Nam Co region, particularly during the non-monsoon period, which is useful to interpret the elemental records in the TP ice cores and lake sediments.