Abstract

Abstract. This study reports the concentrations and potential sources of speciated atmospheric mercury at the Shangri-La Atmosphere Watch Regional Station (SAWRS), a pristine high-altitude site (3580 m a.s.l.) in Tibetan Plateau, China. Total gaseous mercury (TGM, defined as the sum of gaseous elemental mercury, GEM, and gaseous oxidized mercury, GOM), GOM and particulate-bound mercury (PBM) were monitored from November 2009 to November 2010 to investigate the characteristics and potential influence of the Indian summer monsoon (ISM) and the Westerlies on atmospheric transport of mercury. The mean concentrations (± standard deviation) of TGM, PBM and GOM were 2.55 ± 0.73 ng m−3, 38.82 ± 31.26 pg m−3 and 8.22 ± 7.90 pg m−3, respectively. A notable seasonal pattern of TGM concentrations was observed with higher concentrations at the beginning and the end of the ISM season. High TGM concentrations (> 2.5 ng m−3) were associated with the transport of dry air that carried regional anthropogenic emissions from both Chinese domestic and foreign (e.g., Myanmar, Bay of Bengal, and northern India) sources based on analysis of HYSPLIT4 back trajectories. Somewhat lower PBM and GOM levels during the ISM period were attributed to the enhanced wet scavenging. The high GOM and PBM were likely caused by local photo-chemical transformation under low RH and the domestic biofuel burning in cold seasons.

Highlights

  • Mercury (Hg) is a persistent toxic pollutant released to the atmosphere from both anthropogenic and natural sources (Pirrone et al, 1996; Pirrone et al, 2001; Carpi and Lindberg, 1998)

  • We report the characteristics of the speciated atmospheric Hg at the Shangri-La Atmosphere Watch Regional Station (SAWRS) and analyze the potential source regions that contributed to the observed concentrations

  • Spikes of high Total gaseous mercury (TGM) concentrations were observed from late April through early May (5.87 ng m−3), from late June through early July (4.58 ng m−3), and in late September (4.74 ng m−3)

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Summary

Introduction

Mercury (Hg) is a persistent toxic pollutant released to the atmosphere from both anthropogenic and natural sources (Pirrone et al, 1996; Pirrone et al, 2001; Carpi and Lindberg, 1998). Hg interconverts among GEM, gaseous oxidized mercury (GOM) and particulate-bound mercury (PBM) and enters terrestrial and aquatic ecosystems in remote areas via dry and wet deposition (Johansson et al, 2001). Typical concentrations of GEM, GOM and PBM measured at remote sites are in the ranges of 1–4 ng m−3, 3–70 pg m−3 and 7–100 pg m−3, respectively (Valente et al, 2007; Pfaffhuber et al, 2012). In the Arctic, the GEM, PBM and GOM median concentrations are 1.6 ng m−3, 11.3 pg m−3 and 3.2 pg m−3, respectively (Steffen et al, 2014). In Antarctica, the mean annual GEM concentration of 0.93 ± 0.19 ng m−3 is in good agreement with recent southern hemispheric measurements (Pfaffhuber et al, 2012)

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