New evidence for atmospheric mercury transformations in the marine boundary layer from stable mercury isotopes

Ben Yu,Hongwei Liu,Yong Liang,Guibin Jiang,Qian Liu,Yongguang Yin,Cailing Xiao,Linlin Wang,Jianbo Shi,Lin Yang,Ligang Hu

doi:10.5194/acp-20-9713-2020

Abstract

Abstract. The marine boundary layer (MBL) is the largest transport place and reaction vessel of atmospheric mercury (Hg). The transformations of atmospheric Hg in the MBL are crucial for the global transport and deposition of Hg. Herein, Hg isotopic compositions of total gaseous mercury (TGM) and particle-bound Hg (PBM) collected during three cruises to Chinese seas in summer and winter were measured to reveal the transformation processes of atmospheric Hg in the MBL. Unlike the observation results at inland sites, isotopic compositions of TGM in the MBL were affected not only by mixing continental emissions but also largely by the oxidation of Hg0 primarily derived by Br atoms. Δ199Hg values of TGM were significantly positively correlated with air temperature in summer, indicating that processes inducing positive mass-independent fractionation of odd isotopes in TGM could be more active at low temperatures, while the relative processes might be weak in winter. In contrast, the positive Δ199Hg and high ratios of Δ199Hg∕Δ201Hg in PBM indicated that alternative oxidants other than Br or Cl atoms played a major role in the formation of Hg(II) in PBM, likely following the nuclear volume effect. Our results suggest the importance of local Hg environmental behaviors caused by an abundance of highly reactive species and provide new evidence for understanding the complicated transformations of atmospheric Hg in the MBL.

Highlights

The transport and deposition of atmospheric mercury (Hg) are largely attributed to the transformations among three species, including gaseous elemental Hg (GEM), gaseous oxidized Hg (GOM), and particle-bound Hg (PBM), because of the different resident times and migration abilities of them in the atmosphere (Schroeder and Munthe, 1998)
total gaseous mercury (TGM) collected during the 2016-winter cruise, which was supposed to be largely impacted by anthropogenic emissions from mainland China based on the monsoon (Fig. S1), showed positive δ202Hg and negative
Isotopic compositions in TGM collected during the 2016-winter cruise suggested a limited influence from the anthropogenic emissions that diluted in the clean air in the marine boundary layer (MBL)

Summary

Introduction

The transport and deposition of atmospheric mercury (Hg) are largely attributed to the transformations among three species, including gaseous elemental Hg (GEM), gaseous oxidized Hg (GOM), and particle-bound Hg (PBM), because of the different resident times and migration abilities of them in the atmosphere (Schroeder and Munthe, 1998). The transformations of atmospheric Hg are crucial to the global cycling of Hg. The marine boundary layer (MBL) is the largest transport area and reaction vessel for atmospheric Hg on Earth. The marine boundary layer (MBL) is the largest transport area and reaction vessel for atmospheric Hg on Earth It accepts 3400 Mg yr−1 of Hg from ocean via evasion and deposits 3800 Mg yr−1 of Hg into the ocean (UN Environment, 2019). Sampling in the MBL provides an opportunity to study atmospheric Hg transformations, e.g., the scavenging of GEM or the generation of GOM (Hedgecock and Pirrone, 2001; Hedgecock and Pirrone, 2004; Laurier et al, 2003; Sprovieri et al, 2010; WeissPenzias et al, 2003; De Simone et al, 2013; Holmes et al, 2010; Peleg et al, 2015), occurring outside of the influences of continental emissions.

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