Dust dominates the summer melting of glacier ablation zones on the northeastern Tibetan Plateau.

Dust and black carbon (BC) can darken snow and ice surface and play pivotal roles in glacier mass loss. Thus, a quantitative assessment of their contributions to glacier summer melting is critical. During the summer of 2018, surface snow and ice were sampled, and the albedo and mass balance were continuously measured in the ablation zone of Laohugou Glacier No. 12 in the western Qilian Mountains. The physical properties of dust and BC were measured in the laboratory, and their impacts on glacier surface albedo reduction and melting were simulated. The results indicate that the ice surface in the ablation zone was enriched with substantial amounts of particles, and the average particle concentrations of these samples were hundreds of times higher than those of fresh snow. The BC mass absorption cross-sections (MACs) ranged from 3.1 m2 g-1 at 550 nm for dirty ice to 4.6 m2 g-1 for fresh snow, largely owing to meltwater percolation and particle collapse. The spectral variations in dust MACs were significantly different in the visible light bands and near-infrared bands from those in the other areas. Moreover, the two-layer surface energy and mass balance model with the new albedo parameterization formula was validated and agreed well with the experimental measurements of spectral albedo, broadband albedo, and mass balance. BC and dust combined resulted in 26.7 % and 54.4 % of the total mass loss on the cleaner and dirtier (particle enriched) surfaces in the ablation zone, respectively, compared to particle-free surfaces, and although both impurities played vital roles, dust was the more prominent factor in accelerating glacier melting on the northeastern Tibetan Plateau. This study emphasizes the importance of dust in cryosphere changes where Tibetan glaciers are strongly affected by Asian dust deposition.

Black carbon and dust in the Third Pole glaciers: Revaluated concentrations, mass absorption cross-sections and contributions to glacier ablation.

In snow and ice, light-absorbing particles (LAPs), such as black carbon (BC) and dust, accelerate the melting of Third Pole glaciers (TPGs). In this study, we revaluated LAP concentrations in the snow pits of TPGs (SP-TPGs), measured LAP mass absorption cross-sections (MACs), and simulated their effects on glacier darkening and melting based on the Spectral Albedo Model for Dirty Snow and a surface energy and mass balance model. The results indicated that because of their short distances to emission sources, the average BC concentrations measured in snow pits in the periphery of Third Pole were much higher than those measured in the inland Tibetan Plateau, and the average dust concentrations generally decreased from north to south. The average MACs of BC in the SP-TPGs varied from 3.1 to 7.7 m2 g-1 at 550 nm, most of the average spectral values were comparable in the visible and near-infrared bands to those calculated by Mie theory, except those in Urumqi Glacier No. 1 (UR), Syek Zapadniy Glacier (SZ), and Laohugou Glacier No.12 (LH), while the average spectral MACs of dust in the SP-TPGs were considerably smaller in magnitude than most of the variations measured in other regions. Compared with the pure snow surfaces, BC and dust played comparable roles in reducing albedo in UR, SZ, LH, and Renlongba Glacier, whereas BC was the most prominent absorber in the other glaciers. The combined effect of BC and dust accelerated melting by 30.4-345.9 mm w.e. (19.7-45.3% of the total mass balance) through surface albedo darkening (0.06-0.17) and increased radiation absorption (25.8-65.7 W m-2) within one month of the ablation season. This study provides a new data set of LAP concentrations and MACs and helps to clarify the roles of these factors in the cryospheric environment of the Third Pole.

Monsoon-driven transport of organochlorine pesticides and polychlorinated biphenyls to the Tibetan Plateau: three year atmospheric monitoring study.

Due to the influence of the Indian monsoon system, air mass transport in and to the Tibetan Plateau shows obvious seasonality. In order to assess the responses of atmospheric concentrations of persistent organic pollutants (POPs) to the Indian Monsoon fluctuation patterns, a three year air monitoring program (2008-2011) was conducted in an observation station close to the Yarlung Tsangpo Grand Canyon, southeastern Tibetan Plateau. The air concentrations of polychlorinated biphenyls (PCBs) and hexachlorocyclohexanes (HCHs) are generally comparable to those of other remote regions, whereas the concentrations of DDTs are much higher than reported for the polar regions, the North American Rocky Mountains, and the European Alps. The concentrations of DDTs and PCBs were strongly linked to the cyclic patterns of the Indian monsoon, displaying higher values in the monsoon season (May-September) and lower values in the nonmonsoon season (November-March). A "bimodal" pattern was observed for α- and γ-HCH, with higher concentrations in spring and autumn and lower concentrations in the summer (monsoon season). Rain scavenging in the monsoon season likely resulted in the lower HCH concentrations in the atmosphere. This paper sheds lights on the role the Indian monsoon plays on the atmospheric transport of POPs to the Tibetan Plateau.