Atmospheric wet and litterfall mercury deposition at urban and rural sites in China

Xuewu Fu,Jun Zhou,Haiyu Yan,Xiaofang Lang,Ben Yu,Xinbin Feng,Che-Jen Lin,Xu Yang,Hui Zhang

doi:10.5194/acp-16-11547-2016

Abstract

Abstract. Mercury (Hg) concentrations and deposition fluxes in precipitation and litterfall were measured at multiple sites (six rural sites and an urban site) across a broad geographic area in China. The annual deposition fluxes of Hg in precipitation at rural sites and an urban site were 2.0 to 7.2 and 12.6 ± 6.5 µg m−2 yr−1, respectively. Wet deposition fluxes of Hg at rural sites showed a clear regional difference with elevated deposition fluxes in the subtropical zone, followed by the temporal zone and arid/semi-arid zone. Precipitation depth is the primary influencing factor causing the variation of wet deposition. Hg fluxes through litterfall ranged from 22.8 to 62.8 µg m−2 yr−1, higher than the wet deposition fluxes by a factor of 3.9 to 8.7 and representing approximately 75 % of the total Hg deposition at the forest sites in China. This suggests that uptake of atmospheric Hg by foliage is the dominant pathway to remove atmospheric Hg in forest ecosystems in China. Wet deposition fluxes of Hg at rural sites of China were generally lower compared to those in North America and Europe, possibly due to a combination of lower precipitation depth, lower GOM concentrations in the troposphere and the generally lower cloud base heights at most sites that wash out a smaller amount of GOM and PBM during precipitation events.

Highlights

Mercury (Hg), especially its methylated form, is a potent neurotoxin to humans and wildlife
This study aims to better understand the spatial distributions of Hg deposition and mass balance of atmospheric Hg in China
The volume-weighted mean (VWM) Hg concentrations in precipitation at the remote sites varied from 3.7 to 7.7 ng L−1, with the highest VWM Hg concentration observed at the BYBLK site and the lowest at the MAL and MDM sites

Summary

Introduction

Mercury (Hg), especially its methylated form, is a potent neurotoxin to humans and wildlife. GEM has an atmospheric residence time of several months to a year and spreads globally before being converted to other forms and deposited to the earth’s surface (Holmes et al, 2010; Driscoll et al, 2013; Amos et al, 2015). GOM and PBM have much higher water solubility and reactivity, and are readily deposited via wet and dry deposition pathways. Direct and legacy anthropogenic emissions represent the predominant (∼ 2/3) sources of Hg in the atmosphere (Seigneur et al, 2004; Selin et al, 2007; Pirrone et al, 2010), and account for most of the deposition of Hg to the earth’s surface (Selin et al, 2008; Amos et al, 2013).

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