New evidence for atmospheric mercury transformations in the marine boundary layer from stable mercury isotopes
2020
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.
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