Inland Tibetan Plateau Research Articles

Organic aerosols in the inland Tibetan Plateau: New insights from molecular tracers

Aerosols affect the radiative forcing of the global climate and cloud properties. Organic aerosols are among the most important, yet least understood, components of the sensitive Tibetan Plateau atmosphere. Here, the concentration of and the seasonal and diurnal variations in biomass burning and biogenic aerosols, and their contribution to organic aerosols in the inland Tibetan Plateau were investigated using molecular tracers. Biomass burning tracers including levoglucosan and its isomers, and aromatic acids showed higher concentrations during winter than in summer. Molecular tracers of primary and secondary biogenic organic aerosols were more abundant during summer than those in winter. Meteorological conditions were the main factors influencing diurnal variations in most organic molecular tracers during both seasons. According to the tracer-based method, we found that biogenic secondary organic aerosols (38.5 %) and fungal spores (14.4 %) were the two dominant contributors to organic aerosols during summer, whereas biomass burning (15.4 %) was an important aerosol source during winter at remote continental background site. Results from the positive matrix factor source apportionment also demonstrate the importance of biomass burning and biogenic aerosols in the inland Tibetan Plateau. During winter, the long-range transport of biomass burning from South Asia contributes to organic aerosols. In contrast, the precursors, biogenic secondary organic aerosols, and fungal spores from local emissions/long-range transport are the major sources of organic aerosols during summer. Further investigation is required to distinguish between local emissions and the long-range transport of organic aerosols. In-depth insights into the organic aerosols in the Tibetan Plateau are expected to reduce the uncertainties when evaluating aerosol effects on the climate system in the Tibetan Plateau.

Insight into the relationships between total suspended particles and mercury in meltwater in a typical glacierized basin in the inland Tibetan Plateau

Mercury (Hg) released by melting glaciers is likely to bind to suspended particles in meltwater runoff, posing potential risks to downstream ecosystems. The rapidly receding glaciers on the Tibetan Plateau promote the export of total suspended particles (TSP), increasing the uncertainty of Hg export released by glacier melting. To investigate the relationships between TSP and Hg, a multimedia sampling campaign was conducted in July 2020 in the Kuoqionggangri glacier region of the Lhasa River Valley No. 1 glacierized basin located in the inland Tibetan Plateau. Samples from glacier snow/ice, supraglacial rivers, subglacial rivers, proglacial lakes, and meltwater runoff were obtained, and the relationships between TSP and Hg and their transport in glacier meltwater runoff in the context of glacier retreat were explored. The average TSP concentration of different environmental samples ranged from 9.51 mg/L to 399. 27 mg/L, showing significant differences. The average total Hg (THg) concentrations ranged from 0.52 ng/L to 58.81 ng/L and decreased in the order of snow/ice >runoff> subglacial river > proglacial lake > supraglacial river. Both TSP mass concentration and number concentration have an impact on the diurnal variation in meltwater runoff Hg, and the influence of TSP number concentration is stronger than that of concentration. Sites with high TSP concentrations and quantities tended to have higher Hg concentrations, while TSP particle size had no significant effect on Hg concentration or spatial distribution. Our study further divided the glacier recharge basin into the glacier cover zone, the periglacial zone, and the downstream zone and discussed the potential impact of TSP on Hg transport in each zone. Our analysis highlights that the periglacial zone will expand and activate the resuspension process of river sediments in the warming future, which may increase the export of TSP and Hg downstream.

Composition and sources of heavy metals in aerosol at a remote site of Southeast Tibetan Plateau, China

Knowledge of the elemental composition of aerosols at remote sites is important for evaluating the influence of anthropogenic activities. In this study, the elemental composition and sources of total suspended particles (TSP) at Yaze, a remote site in the southeastern Tibetan Plateau (TP), were investigated. The results showed that the mean elemental concentrations at Yaze were relatively low compared with those in other areas of the TP. Seasonal variations in the studied elements was characterized by low and high concentrations during the monsoon and non-monsoon periods, respectively. The enrichment factors (EFs) for some heavy metals at Yaze were slightly higher than those at Nam Co station (inland TP) but much lower than those at Mt. Yulong (southeastern TP) and in the Indian megacity of Delhi, indicating fewer anthropogenic influences at the study site relative to sites close to severely polluted regions. For the studied elements, three major sources were identified: crustal origins (e.g., Al and Fe), anthropogenic origins (e.g., Zn and Cd) and mixed origins (e.g., As and Bi). Further analysis by potential source contribution functions showed that the local TP was the primary source for elements of crustal origins. Correspondingly, the typical heavy metals were mainly attributed to pollution emitted from anthropogenic activities and transported over long-range from both South and Southeast Asia. This work demonstrates the transport of heavy metals from external sources to remote sites in the southeastern TP. These results are also useful for interpreting the historical profiles of heavy metals in the ice cores of the TP.

Black carbon and organic carbon dataset over the Third Pole

Abstract. The Tibetan Plateau and its surroundings, also known as the Third Pole, play an important role in the global and regional climate and hydrological cycle. Carbonaceous aerosols (CAs), including black carbon (BC) and organic carbon (OC), can directly or indirectly absorb and scatter solar radiation and change the energy balance on the Earth. CAs, along with the other atmospheric pollutants (e.g., mercury), can be frequently transported over long distances into the inland Tibetan Plateau. During the last decades, a coordinated monitoring network and research program named “Atmospheric Pollution and Cryospheric Changes” (APCC) has been gradually set up and continuously operated within the Third Pole regions to investigate the linkage between atmospheric pollutants and cryospheric changes. This paper presents a systematic dataset of BC, OC, water-soluble organic carbon (WSOC), and water-insoluble organic carbon (WIOC) from aerosols (20 stations), glaciers (17 glaciers, including samples from surface snow and ice, snow pits, and 2 ice cores), snow cover (2 stations continuously observed and 138 locations surveyed once), precipitation (6 stations), and lake sediment cores (7 lakes) collected across the Third Pole, based on the APCC program. These data were created based on online (in situ) and laboratory measurements. High-resolution (daily scale) atmospheric-equivalent BC concentrations were obtained by using an Aethalometer (AE-33) in the Mt. Everest (Qomolangma) region, which can provide new insight into the mechanism of BC transportation over the Himalayas. Spatial distributions of BC, OC, WSOC, and WIOC from aerosols, glaciers, snow cover, and precipitation indicated different features among the different regions of the Third Pole, which were mostly influenced by emission sources, transport pathways, and deposition processes. Historical records of BC from ice cores and lake sediment cores revealed the strength of the impacts of human activity since the Industrial Revolution. BC isotopes from glaciers and aerosols identified the relative contributions of biomass and fossil fuel combustion to BC deposition on the Third Pole. Mass absorption cross sections of BC and WSOC from aerosol, glaciers, snow cover, and precipitation samples were also provided. This updated dataset is released to the scientific communities focusing on atmospheric science, cryospheric science, hydrology, climatology, and environmental science. The related datasets are presented in the form of excel files. BC and OC datasets over the Third Pole are available to download from the National Cryosphere Desert Data Center (https://doi.org/10.12072/ncdc.NIEER.db0114.2021; Kang and Zhang, 2021).

Organic Aerosols in the Inland Tibetan Plateau: New Insights from Molecular Tracers

Organic Aerosols in the Inland Tibetan Plateau: New Insights from Molecular Tracers

Impacts of Indian summer monsoon and stratospheric intrusion on air pollutants in the inland Tibetan Plateau

Air pollutants can be transported to the pristine regions such as the Tibetan Plateau, by monsoon and stratospheric intrusion. The Tibetan Plateau region has limited local anthropogenic emissions, while this region is influenced strongly by transport of heavy emissions mainly from South Asia. We conducted a comprehensive study on various air pollutants (PM2.5, total gaseous mercury, and surface ozone) at Nam Co Station in the inland Tibetan Plateau. Monthly mean PM2.5 concentration at Nam Co peaked in April before monsoon season, and decreased during the whole monsoon season (June–September). Monthly mean total gaseous mercury concentrations at Nam Co peaked in July and were in high levels during monsoon season. The Indian summer monsoon acted as a facilitator for transporting gaseous pollutants (total gaseous mercury) but a suppressor for particulate pollutants (PM2.5) during the monsoon season. Different from both PM2.5 and total gaseous mercury variabilities, surface ozone concentrations at Nam Co are primarily attributed to stratospheric intrusion of ozone and peaked in May. The effects of the Indian summer monsoon and stratospheric intrusion on air pollutants in the inland Tibetan Plateau are complex and require further studies.

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.

Mercury biogeochemistry over the Tibetan Plateau: An overview

Since the beginning of the 21st century, our knowledge of the sources and fate of Hg over the Tibetan Plateau (TP), the “Roof of the World,” has been greatly enhanced with growing literature. Here, we reviewed the available literature to obtain a comprehensive understanding of Hg biogeochemistry over the TP. The biogeochemical Hg cycling is characterized by the following features: (1) There are existing but limited local emission sources of anthropogenic Hg in the TP. The Indian Summer Monsoon is an important transporter of atmospheric Hg pollution into the inland TP; (2) “Cold trapping effect” plays an important role in the atmospheric Hg deposition over the TP. Glacier, vegetation, and soil act as important “sinks” of atmospheric Hg pollution; (3) Enhanced anthropogenic activities around the TP, climate warming and glacier melting have the potential impacts to affect the behavior and distribution of Hg; (4) Significant bioaccumulation of MeHg (>100 ng/g) has been found in the Tibetan aquatic food chains. Considering that transboundary transport is responsible for the widespread Hg pollution in the TP, international/regional collaborations regarding Hg emission regulations are needed to reduce the migration of Hg and to mitigate adverse Hg pollution impacts on the TP.

Multi-year monitoring of atmospheric total gaseous mercury at a remote high-altitude site (Nam Co, 4730 m a.s.l.) in the inland Tibetan Plateau region

Abstract. Total gaseous mercury (TGM) concentrations were continuously measured at Nam Co Station, a remote high-altitude site (4730 m a.s.l.), on the inland Tibetan Plateau, China, from January 2012 to October 2014 using a Tekran 2537B instrument. The mean concentration of TGM during the entire monitoring period was 1.33±0.24 ng m−3 (mean ± standard deviation), ranking it as the lowest value among all continuous TGM measurements reported in China; it was also lower than most of sites in the Northern Hemisphere. This indicated the pristine atmospheric environment on the inland Tibetan Plateau. Long-term TGM at the Nam Co Station exhibited a slight decrease especially for summer seasons. The seasonal variation of TGM was characterized by higher concentrations during warm seasons and lower concentrations during cold seasons, decreasing in the following order: summer (1.50±0.20 ng m−3) > spring (1.28±0.20 ng m−3) > autumn (1.22±0.17 ng m−3) > winter (1.14±0.18 ng m−3). Diurnal variations of TGM exhibited uniform patterns in different seasons: the daily maximum was reached in the morning (around 2–4 h after sunrise), followed by a decrease until sunset and a subsequent buildup at night, especially in the summer and the spring. Regional surface reemission and vertical mixing were two major contributors to the temporal variations of TGM while long-range transported atmospheric mercury promoted elevated TGM during warm seasons. Results of multiple linear regression (MLR) revealed that humidity and temperature were the principal covariates of TGM. Potential source contribution function (PSCF) and FLEXible PARTicle dispersion model (WRF-FLEXPART) results indicated that the likely high potential source regions of TGM to Nam Co were central and eastern areas of the Indo-Gangetic Plain (IGP) during the measurement period with high biomass burning and anthropogenic emissions. The seasonality of TGM at Nam Co was in phase with the Indian monsoon index, implying the Indian summer monsoon as an important driver for the transboundary transport of air pollution onto the inland Tibetan Plateau. Our results provided an atmospheric mercury baseline on the remote inland Tibetan Plateau and serve as new constraint for the assessment of Asian mercury emission and pollution.

Glacier Energy and Mass Balance in the Inland Tibetan Plateau: Seasonal and Interannual Variability in Relation to Atmospheric Changes

AbstractThe Tibetan glaciers are greatly affected by the circulations of the westerlies and the Indian summer monsoon (ISM), but the mechanisms remain to be elucidated. In this project, we investigated the surface energy and mass balance of the Qiangtang No.1 Glacier in the inland Tibetan Plateau. Combining 4‐year mass balance and meteorological records near the equilibrium line altitude with an energy‐based mass balance model, we found that the meteorological conditions, which determined the glacier surface ablation and mass accumulation, are critically linked to changes in the intensity of the westerlies and the ISM. The 4‐year mass balance comparisons demonstrated that the enhancement of the ISM in June and July, especially June, greatly increases the mass accumulation but inhibits the glacial ablation in the melt season, shifting the mass balance in a positive direction. Moreover, the occurrence of the westerlies enhancement interrupts the dominance of the ISM in the melt season. The intensified westerlies in the early melt season (June) could not only reduce the mass accumulation but also enhance the mass loss in the following months. In addition, the enhancement of the westerlies in the main melt season (July) could also greatly influence the local meteorological conditions, with lower temperatures and humidity but higher wind speeds. Such meteorological changes significantly reduce glacial ablation because more energy is consumed by sublimation and/or evaporation, rather than surface melting. These findings will enhance our understanding of the mechanisms underlying glacier changes and their relationships with the westerlies and the ISM in the inland Tibetan Plateau.

Fossil Fuel Combustion Emission From South Asia Influences Precipitation Dissolved Organic Carbon Reaching the Remote Tibetan Plateau: Isotopic and Molecular Evidence

AbstractThe dissolved organic carbon in precipitation (water‐soluble organic carbon, WSOC) can provide a carbon subsidy to receiving ecosystems. The concentrations, isotopic signatures (δ13C/Δ14C), and molecular signatures (transform ion cyclotron mass spectrometry) of WSOC being delivered to Nam Co—a remote site on the inland Tibetan Plateau (TP)—were compared to those of WSOC in the snowpack, and in wet deposition from urban cities fringing the TP. The average WSOC concentration at Nam Co (1.0 ± 0.9 mg C L−1) was lower than for the large cities (1.6 to 2.3 mg C L−1) but higher than in the snowpack samples (0.26 ± 0.09 mg C L−1). Based upon radiocarbon data, it is estimated that 15 ± 6% of Nam Co WSOC was fossil derived, increasing to 20 ± 8% for snowpack WSOC, 29 ± 4% for Lhasa WSOC, and 34 ± 8% for the three cities. Transform ion cyclotron mass spectrometry results revealed that the abundance of dissolved black carbon and sulfur‐containing molecules of WSOC increased in the order Nam Co < snow pack < urban. The enrichment in 14C and depletion in dissolved black carbon and sulfurous organic molecules of Nam Co WSOC was suggestive of low, but still detectable inputs of fossil‐derived organics to WSOC on the remote TP. Backward air mass trajectories for the precipitation events at Nam Co suggested that the fossil fuel contributions to WSOC in Nam Co region originated mainly from South Asia. This study provides novel radiocarbon age, chemistry, and source evidence that anthropogenic WSOC is delivered to the remote TP, one of the most remote regions on Earth.

Mercury speciation and distribution in a glacierized mountain environment and their relevance to environmental risks in the inland Tibetan Plateau

Glacierized mountain environments can preserve and release mercury (Hg) and play an important role in regional Hg biogeochemical cycling. However, the behavior of Hg in glacierized mountain environments and its environmental risks remain poorly constrained. In this research, glacier meltwater, runoff and wetland water were sampled in Zhadang-Qugaqie basin (ZQB), a typical glacierized mountain environment in the inland Tibetan Plateau, to investigate Hg distribution and its relevance to environmental risks. The total mercury (THg) concentrations ranged from 0.82 to 6.98ng·L−1, and non-parametric pairwise multiple comparisons of the THg concentrations among the three different water samples showed that the THg concentrations were comparable. The total methylmercury (TMeHg) concentrations ranged from 0.041 to 0.115ng·L−1, and non-parametric pairwise multiple comparisons of the TMeHg concentrations showed a significant difference. Both the THg and MeHg concentrations of water samples from the ZQB were comparable to those of other remote areas, indicating that Hg concentrations in the ZQB watershed are equivalent to the global background level. Particulate Hg was the predominant form of Hg in all runoff samples, and was significantly correlated with the total suspended particle (TSP) and not correlated with the dissolved organic carbon (DOC) concentration. The distribution of mercury in the wetland water differed from that of the other water samples. THg exhibited a significant correlation with DOC as well as TMeHg, whereas neither THg nor TMeHg was associated with TSP. Based on the above findings and the results from previous work, we propose a conceptual model illustrating the four Hg distribution zones in glacierized environments. We highlight that wetlands may enhance the potential hazards of Hg released from melting glaciers, making them a vital zone for investigating the environmental effects of Hg in glacierized environments and beyond.

Surface ozone at Nam Co in the inland Tibetan Plateau: variation, synthesis comparison and regional representativeness

Abstract. Ozone is an important pollutant and greenhouse gas, and tropospheric ozone variations are generally associated with both natural and anthropogenic processes. As one of the most pristine and inaccessible regions in the world, the Tibetan Plateau has been considered as an ideal region for studying processes of the background atmosphere. Due to the vast area of the Tibetan Plateau, sites in the southern, northern and central regions exhibit different patterns of variation in surface ozone. Here, we present continuous measurements of surface ozone mixing ratios at Nam Co Station over a period of ∼ 5 years (January 2011 to October 2015), which is a background site in the inland Tibetan Plateau. An average surface ozone mixing ratio of 47.6 ± 11.6 ppb (mean ± standard deviation) was recorded, and a large annual cycle was observed with maximum ozone mixing ratios in the spring and minimum ratios during the winter. The diurnal cycle is characterized by a minimum in the early morning and a maximum in the late afternoon. Nam Co Station represents a background region where surface ozone receives negligible local anthropogenic emissions inputs, and the anthropogenic contribution from South Asia in spring and China in summer may affect Nam Co Station occasionally. Surface ozone at Nam Co Station is mainly dominated by natural processes involving photochemical reactions, vertical mixing and downward transport of stratospheric air mass. Model results indicate that the study site is affected differently by the surrounding areas in different seasons: air masses from the southern Tibetan Plateau contribute to the high ozone levels in the spring, and enhanced ozone levels in the summer are associated with air masses from the northern Tibetan Plateau. By comparing measurements at Nam Co Station with those from other sites on the Tibetan Plateau, we aim to expand the understanding of ozone cycles and transport processes over the Tibetan Plateau. This work may provide a reference for future model simulations.

The role of melting alpine glaciers in mercury export and transport: An intensive sampling campaign in the Qugaqie Basin, inland Tibetan Plateau

Glaciers, particularly alpine glaciers, have been receding globally at an accelerated rate in recent decades. The glacial melt-induced release of pollutants (e.g., mercury) and its potential impact on the atmosphere and glacier-fed ecosystems has drawn increasing concerns. During 15th–20th August, 2011, an intensive sampling campaign was conducted in Qugaqie Basin (QB), a typical high mountain glacierized catchment in the inland Tibetan Plateau, to investigate the export and transport of mercury from glacier to runoff. The total mercury (THg) level in Zhadang (ZD) glacier ranged from <1 to 20.8 ng L−1, and was slightly higher than levels measured in glacier melt water and the glacier-fed river. Particulate Hg (PHg) was the predominant form of Hg in all sampled environmental matrices. Mercury concentration in Qugaqie River (QR) was characterized by a clear diurnal variation which is linked to glacier melt. The estimated annual Hg exports by ZD glacier, the upper river basin and the entire QB were 8.76, 7.3 and 157.85 g, respectively, with respective yields of 4.61, 0.99 and 2.74 μg m−2 yr−1. Unique landforms and significant gradients from the glacier terminus to QB estuary might promote weathering and erosion, thereby controlling the transport of total suspended particulates (TSP) and PHg. In comparison with other glacier-fed rivers, QB has a small Hg export yet remarkably high Hg yield, underlining the significant impact of melting alpine glaciers on regional Hg biogeochemical cycles. Such impacts are expected to be enhanced in high altitude regions under the changing climate.

Variations in annual accumulation recorded in a Laohugou ice core from the northeastern Tibetan Plateau and their relationship with atmospheric circulation

Annual accumulation was reconstructed for a period from 1960 to 2006 using a 21.2-m ice core from the firn basin of Laohugou (LHG) Glacier No. 12 on the northeastern Tibetan Plateau (TP). Significant periodicity of LHG accumulation variations was identified as a quasi-3-year period in accordance with the oscillation of precipitation in the northwestern China, especially the Hexi Corridor. Furthermore, the relationships of LHG accumulation with atmospheric circulation and moisture sources were investigated. LHG accumulation was positively correlated with the 500-hPa geopotential height and pressure in Central Asia, as well as the autumn Northern Atlantic Oscillation, suggesting that the Westerlies may transport moisture to the LHG region and enhance precipitation. In addition, a negative relationship between LHG accumulation and meridional wind indicated that an intense Mongolian cyclone caused by a strong meridional wind in the region could block Arctic air masses from the LHG region. Moisture fluxes and backward air mass trajectories suggested that moisture might originate from Central Asia, Southern and the inland TP. The relationship between LHG accumulation and atmospheric circulation provides an opportunity to reconstruct the history of atmospheric circulation using a deep ice core record.

First field-based atmospheric observation of the reduction of reactive mercury driven by sunlight

Hourly speciated measurements of atmospheric mercury made in a remote, high-altitude site in the Tibetan Plateau revealed the first field observations of the reduction of reactive mercury in the presence of sunlight in the atmosphere. Measurements were collected over four winter months on the shore of Nam Co Lake in the inland Tibetan Plateau. The data was analyzed to identify sources and atmospheric transformations of the speciated mercury compounds. The absence of local anthropogenic sources provided a unique opportunity to examine chemical transformations of mercury. An optimization algorithm was used to determine the parameters of a chemical box model that would match the measured reactive mercury concentrations. This required the presence of a photolytic reduction reaction previously observed in laboratory studies and in power plant plumes. In addition, the model estimated the role of vertical mixing in diluting reactive gaseous mercury during the day, and the role of bromine chemistry in oxidizing gaseous elemental mercury to produce reactive gaseous mercury. This work provides further evidence of the need to add the photolytic reduction reaction of oxidized mercury into atmospheric transport models in order to better simulate mercury deposition.

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

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.

A 500 year atmospheric dust deposition retrieved from a Mt. Geladaindong ice core in the central Tibetan Plateau

A 147-m ice core was retrieved from Guoqu Glacier (33.58°N, 91.18°E, 5750ma.s.l.) during the Sino–US cooperation expedition on Mt. Geladaindong in the central Tibetan Plateau (TP). In this study, we investigated the high-resolution of atmospheric dust records by using the insoluble particles and crustal ions (Ca2+ and Mg2+) from the upper 109.93m segments, covering the period of 1477 to 1982AD. There existed positive correlations among the ice core dust records themselves and with the dust days from the nearby meteorological stations during the recent decades, indicating that the insoluble particles and crustal ions in the ice core can be used to reconstruct the past atmospheric dust variability. During the past 500years, the insoluble particles and crustal ions showed high concentrations in the 18th to 19th centuries and low concentrations in the 20th century, corresponding to low and high precipitation in the potential dust source regions. The ice core dust records were positively correlated with the zonal wind and the winter North Atlantic Oscillation (NAO) index, suggesting that NAO may be teleconnected to dust entrainment over the inland TP. This long-term ice core provided an approach to understand the atmospheric dust variability in the central TP during the last 500years.

Yak dung combustion aerosols in the Tibetan Plateau: Chemical characteristics and influence on the local atmospheric environment

The study of the source areas of atmospheric pollutants in the Tibetan Plateau (TP) – one of the most remote regions in the world – has raised a great deal of concern. It is generally considered that the majority of pollutants in this region are transported from outside the TP. This research investigated the water soluble elements and carbonaceous matter from aerosols emitted from yak dung combustion by local residents and re-analyzed previous OC and BC data at Nam Co — a remote area of the TP. The compositions of the water soluble elements of the studied aerosols were similar to those in precipitation and snow samples of the region under investigation. Some heavy metal elements (e.g. Cd and As) even had higher enrichment factor (EF) values (1793 and 2355, respectively) compared to those in precipitation and snow samples, implying that previously reported high EF values for precipitation and snow did not completely reflect the long-range transported pollutants from outside the TP. Accordingly, the contributions of local sources needed to be considered. Organic carbon (OC) and black carbon (BC) accounted for 55.2% and 3.63% of the studied aerosol, respectively. The OC/BC ratio of the studied aerosols was close to the corresponding value for the outdoor aerosols, further indicating the influence of local sources on the atmosphere of Nam Co. It was proposed that air masses from South Asia cause high BC concentrations in the Nam Co region. It was, however, discovered that air masses from the TP itself also induce high BC concentrations, suggesting that not all the BC of Nam Co was transported from South Asia. Therefore, it is proposed that pollutants of atmospheric aerosols of the Nam Co region were derived from a variety of sources from both the TP and outside. In other words, the influence of yak dung burning by local residents on the atmosphere of the TP cannot be overlooked. Correspondingly, long-range transported pollutants can penetrate into the inland TP only when intensified pollution events occur in South Asia.

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

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.