Monsoon-facilitated characteristics and transport of atmospheric mercury at a high-altitude background site in southwestern China

Hui Zhang,Xinbin Feng,Che-Jen Lin,Xuewu Fu,Lihai Shang,Cynthia Lin,Yiping Zhang

doi:10.5194/acp-16-13131-2016

Abstract

Abstract. To better understand the influence of monsoonal climate and transport of atmospheric mercury (Hg) in southwestern China, measurements of total gaseous mercury (TGM, defined as the sum of gaseous elemental mercury, GEM, and gaseous oxidized mercury, GOM), particulate bound mercury (PBM) and GOM were carried out at Ailaoshan Station (ALS, 2450 m a.s.l.) in southwestern China from May 2011 to May 2012. The mean concentrations (± SD) for TGM, GOM and PBM were 2.09 ± 0.63, 2.2 ± 2.3 and 31.3 ± 28.4 pg m−3, respectively. TGM showed a monsoonal distribution pattern with relatively higher concentrations (2.22 ± 0.58 ng m−3, p = 0.021) during the Indian summer monsoon (ISM, from May to September) and the east Asia summer monsoon (EASM, from May to September) periods than that (1.99 ± 0.66 ng m−3) in the non-ISM period. Similarly, GOM and PBM concentrations were higher during the ISM period than during the non-ISM period. This study suggests that the ISM and the EASM have a strong impact on long-range and transboundary transport of Hg between southwestern China and south and southeast Asia. Several high TGM events were accompanied by the occurrence of northern wind during the ISM period, indicating anthropogenic Hg emissions from inland China could rapidly increase TGM levels at ALS due to strengthening of the EASM. Most of the TGM and PBM events occurred at ALS during the non-ISM period. Meanwhile, high CO concentrations were also observed at ALS, indicating that a strong south tributary of westerlies could have transported Hg from south and southeast Asia to southwestern China during the non-ISM period. The biomass burning in southeast Asia and anthropogenic Hg emissions from south Asia are thought to be the source of atmospheric Hg in remote areas of southwestern China during the non-ISM period.

Highlights

Mercury (Hg), because of its volatility and long residence time in atmosphere, can transport a long distance with air mass from anthropogenic Hg emission regions to remote areas (Schroeder and Munthe, 1998; Pirrone et al, 2010)
We present the observations of TGM, GOM and particulate bound mercury (PBM) during the ISM and non-ISM periods at Ailaoshan Station (ALS), and discuss the transboundary transport characteristics using backward trajectory analysis
There were several peaks that appeared during the non-ISM period, which could have been caused by different sources than those during the ISM period

Summary

Introduction

Mercury (Hg), because of its volatility and long residence time in atmosphere, can transport a long distance with air mass from anthropogenic Hg emission regions to remote areas (Schroeder and Munthe, 1998; Pirrone et al, 2010). The monsoonal climate has the potential to strongly affect the transport and distribution of atmospheric Hg in monsoon regions, such as east and south Asia. The onset of ISM in May causes air masses, originating from the Indian Ocean, to overpass south and southeast Asia, and move northeastwardly to mainland China. Air pollutants such as SO2 and CO travel into mainland China via air transport caused by the ISM (Xu et al, 2009; Bonasoni et al, 2010; Lin et al, 2013). During the monsoon period (from May to September), the warm and moist air masses from the Pacific Ocean sweep through the coastal area of China into inland China, Published by Copernicus Publications on behalf of the European Geosciences Union

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