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

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.

Stable Mercury Isotopes Revealing Photochemical Processes in the Marine Boundary Layer

“…The δ 202 Hg in the TGM was conspicuously higher than that in PBM (TGM: −0.09 ± 0.48‰, PBM: −0.80 ± 0.58‰, mean ± 1 SD). In addition, the variation range of δ 202 Hg in PBM reported in this study was similar to that reported by Yu et al (2020). These results may indicate the contribution of Hg 0 oxidation to PBM collected in this study.…”

“…Previous studies have reported that continental anthropogenic emissions have an important influence on PBM collected at coastal sites and offshore boundary layers (Demers et al, 2015;Fu et al, 2018Fu et al, , 2019Rolison et al, 2013;Yu et al, 2016Yu et al, , 2020. Therefore, the contents of eight heavy metals (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) in each TSP sample were measured using an ICP-MS (NexION 2000C, PerkinElmer) to estimate the contributions of continental anthropogenic emissions to PBM.…”

“…Coastal PBM samples are largely affected by anthropogenic emissions; hence, their isotopic characteristics record the signatures from both MBL atmospheric processes and anthropogenic emissions (Demers et al, 2015;Fu et al, 2018Fu et al, , 2019Rolison et al, 2013;Yu et al, 2016). Therefore, cruise sampling (off the coast) can more effectively determine the atmospheric processes influencing PBM in the MBL relative to onshore sampling (Yu et al, 2020).…”

Mercury isotopic compositions in fine particles and offshore surface seawater in a coastal area of East China: Implication for Hg sources and atmospheric transformations

“…4, 2018 from the CX. The remarkable odd-MIF of HgPM isotopes has commonly been reported in coastal environment (Rolison et al, 2013;Fu et al, 2019;Yu et al, 2020), thus the positive odd-MIF of HgPM2.5 in this study was likely contributed by enhanced photo-reactions.…”

“…Little literature is available on Hg isotopes of atmospheric samples due to the difficulty in sampling enough Hg mass for isotopes analysis. Even so, Hg isotopic compositions of atmosphere related samples, like speciated Hg, precipitation, and lichen, have been reported in recent years (Carignan et al, 2009;Gratz et al, 2010;Sherman et al, 2010;Chen et al, 2012;Rolison et al, 2013;Demers et al, 2013Demers et al, , 2015Fu et al, 2016Fu et al, , 2018Fu et al, , 2019Yu et al, 2016Yu et al, , 2020. Many studies have measured Hg isotopes in PM to investigate its potential sources and transformation processes in the atmosphere.…”