Atmospheric pollution for trace elements in the remote high-altitude atmosphere in central Asia as recorded in snow from Mt. Qomolangma (Everest) of the Himalayas

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Abstract

A series of 42 snow samples covering over a one-year period from the fall of 2004 to the summer of 2005 were collected from a 2.1-m snow pit at a high-altitude site on the northeastern slope of Mt. Everest. These samples were analyzed for Al, V, Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Sr, Cd, Sb, Pb, and Bi in order to characterize the relative contributions from anthropogenic and natural sources to the fallout of these elements in central Himalayas. Our data were also considered in the context of monsoon versus non-monsoon seasons. The mean concentrations of the majority of the elements were determined to be at the pg g 1 level with a strong variation in concentration with snow depth. While the mean concentrations of most of the elements were significantly higher during the non-monsoon season than during the monsoon season, considerable variability in the trace element inputs to the snow was observed during both periods. Cu, Zn, As, Cd, Sb, and Bi displayed high crustal enrichment factors (EFc) in most samples, while Cr, Ni, Rb, and Pb show high EFc values in some of the samples. Our data indicate that anthropogenic inputs are potentially important for these elements in the remote high-altitude atmosphere in the central Himalayas. The relationship between the EFc of each element and the Al concentration indicates that a dominant input of anthropogenic trace elements occurs during both the monsoon and non-monsoon seasons, when crustal contribution is relatively minor. Finally, a comparison of the trace element fallout fluxes calculated in our samples with those recently obtained at Mont Blanc, Greenland, and Antarctica provides direct evidence for a geographical gradient of the atmospheric pollution with trace elements on a global scale.

Introduction

Greenland and Antarctic snow and ice records have provided historical indications of changes in the occurrence of toxic trace elements in the atmosphere in response to anthropogenic emissions of such elements. Among the most interesting results is the oldest hemispheric scale atmospheric pollution in the Northern Hemisphere for Pb and Cu during the Greco-Roman times, two millennia before the Industrial Revolution, especially due to ancient mining and smelting activities (Hong et al., 1994, Hong et al., 1996, Rosman et al., 1997). The atmospheric pollution from the mid-1700s to present times has also been documented for various heavy metals, including Pb, Cd, Cu, and Zn (Murozumi et al., 1969, Boutron et al., 1991, Candelone et al., 1995), Hg (Boutron et al., 1998), Pt, Pd and Rh (Barbante et al., 2001a). Reliable Antarctic snow and ice records have provided evidence that the natural cycles of trace elements such as Cr, Cu, Zn, Ag, Pb, Bi, and U have been greatly perturbed in the recent decades even in the remote Antarctic atmosphere. This is primarily due to the long-range transport of manmade pollutants from the surrounding source areas such as South America, South Africa, and Australia (Rosman et al., 1994, Wolff and Suttie, 1994, Wolff et al., 1999, Planchon et al., 2002, Planchon et al., 2003, Vallelonga et al., 2002).

Although data obtained from Greenland and Antarctic snow and ice have shown that environmental pollution by trace elements has become global, the spatial data on the occurrence of trace elements in temperate to low-latitude snow and ice are required to better characterize the extent of human impact on natural geochemical cycles of these elements. Recently, several studies have reported changes in the occurrences of trace elements related to human activities in dated snow and ice from the Alps and high-altitude Bolivian ice cap (Van de Velde et al., 1999b, Van de Velde et al., 2000a, b; Rosman et al., 2000, Barbante et al., 2001a, Barbante et al., 2001b, Barbante et al., 2002, Schwikowski et al., 2004, Hong et al., 2004a).

Our understanding of the changing occurrence of trace elements in snow and ice from mid-latitude areas in Asia is of special interest, because the rapid economic growth and industrialization have occurred during the past decades, resulting in elevated levels of anthropogenic pollutants in the atmosphere (Lelieveld et al., 2001, Fang et al., 2005). Indeed, Asia is now the single largest source of anthropogenic trace element emissions to the atmosphere in the world (Pacyna and Pacyna, 2001). Very recently, the trace elements concentrations were measured in snow and firn core samples at high high-altitude sites in the eastern Tien Shan (Li et al., 2007) and on Mt. Muztagh Ata in the eastern Pamirs in northwest China (Li et al., 2006a, Li et al., 2006b), and on Mt. Everest in the Himalayas (Kang et al., 2007, Duan et al., 2007). Such data provided aspects of changing occurrence of various trace elements in snow and ice from one area to another. However, available data are not sufficient to understand the perturbation of atmospheric trace element cycles in Asia, because previous studies dealt with only few elements (Al, V, Cr, Mn, Co, Cu, Zn, Pb, and Bi).

Here, we present new data on 15 trace elements (Al, V, Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Sr, Cd, Sb, Pb and Bi) in successive snow pit samples on the northeastern slope of Mt. Everest in the central Himalayas, spanning a one-year time period. Our data reveal changes in concentration, fallout fluxes and the relative importance of natural and anthropogenic contributions for such elements during monsoon versus non-monsoon periods. Our data are also compared with those obtained in recent Greenland, Antarctic and Mont Blanc snow.

Section snippets

Sampling site

On September 4, 2005, samples were collected at the East Rongbuk Glacier (28°01′08″N, 86°57′48″E, elevation 6576 m asl) on the northeastern slope of Mt. Everest in the central Himalayas (Fig. 1). A shallow snow pit was hand-dug by operators wearing full clean room garments and polyethylene gloves, using acid-cleaned plastic shovels. Approximately 10 cm of snow was then shaved away from the upwind wall using acid-cleaned ultra-clean low-density polyethylene (LDPE) scrapers. A continuous series

Characteristics of the data

The concentrations of 14 trace elements determined in the 42 depth intervals are shown in Fig. 3, which indicate the depth profiles of the observed variations in concentrations of the measured elements. To the best of our knowledge, some of these elements have never been determined in successive snow pit samples collected at a high-altitude location in the Himalayas.

The concentration ranges and the ratios between maximum and minimum concentrations for each element are summarized in Table 2. The

Acknowledgements

We thank all personnel in the field for the sampling during the 2005 Chinese Mt. Everest Expedition. This work was supported in Korea by a research grant (PP07010) from the Korean Research Council of Public Science and Technology. In China, National Basic Research program of China (grant 2007CB411501), the Natural Science Foundation of China (grant 90411003), and the Chinese Academy of Science (grant 100 Talents Project and KZCX3-SW-344) supported this research. In Italy, it was supported

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