Isotopic Composition of Gaseous Elemental Mercury in the Marine Boundary Layer of East China Sea

Abstract

Characterizing the speciation and isotope signatures of atmospheric mercury (Hg) downwind of mainland China is critical to understanding the outflow of Hg emission and the contributing sources. In this study, we measured the concentrations of gaseous elemental mercury (GEM), particulate bound mercury, gaseous oxidized mercury, and the GEM isotopic composition in the marine boundary layer of East China Sea from October 2013 to January 2014. Mean (±1σ) GEM, particulate bound mercury, and gaseous oxidized mercury concentrations were 2.25 ± 1.03 ng/m3, 26 ± 38 pg/m3, and 8 ± 10 pg/m3, respectively. Most events of elevated GEM are associated with the outflow of Hg emissions in mainland China. The 24‐ and 48‐hr integrated GEM samples showed large variations in both δ202Hg (−1.63‰ to 0.34‰) and Δ199Hg (−0.26‰ to −0.02‰). GEM δ202Hg and Δ199Hg were negatively and positively correlated to its atmospheric concentrations, respectively, suggesting a binary physical mixing of regional background GEM and Hg emissions in mainland China. Using a binary mixing model, highly negative δ202Hg (−1.79 ± 0.24‰, 1σ) and near‐zero Δ199Hg (0.02 ± 0.04‰, 1σ) signatures for China GEM emissions are predicted. Such isotopic signatures are significantly different from those found in North America and Europe and the background global/regional atmospheric GEM pool. It is likely that emissions from industrial and residential coal combustion (lacking conventional air pollutant control devices), cement and mercury production, biomass burning, and soil emissions contributed significantly to the estimated isotope signatures of GEM emissions in China.

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

“…Slightly negative 200 Hg and positive 200 Hg values were observed in TGM and PBM samples, respectively (Table 1). These near-zero values were comparable to reported data observed in TGM and PBM at most sites globally (Das et al, 2016;Huang et al, 2015;Fu et al, 2018Fu et al, , 2019aDemers et al, 2013Demers et al, , 2015Enrico et al, 2016). In addition, higher 200 Hg values (0.19±0.18 ‰, 1σ , n = 69) have been commonly observed globally in wet precipitation with Hg(II) as primary species (Chen et al, 2012;Yuan et al, 2018;Gratz et al, 2010;Enrico et al, 2016;Wang et al, 2015).…”

“…S1). and 199 Hg in TGM and PBM samples in this study illustrated with reported isotopic compositions in GEM (Fu et al, 2018) and PBM (Fu et al, 2019a) collected at the Huaniao island site in the East China Sea. The reported data ranges (mean ± SD) of isotopic compositions in TGM/GEM are from remote sites globally (Demers et al, 2015;Yu et al, 2016;Demers et al, 2013;Fu et al, 2016), and PBM data are from inland sites (Yu et al, 2016;Das et al, 2016;Huang et al, 2015Huang et al, , 2016Xu et al, 2017).…”

“…The isotopic compositions in PBM in this study and the similar isotopic compositions in PBM collected at an island site in China (Fu et al, 2019a) were distinguishable from those collected at inland urban and rural sites, suggesting the dominant influences are from the marine environment rather than continental anthropogenic emissions. The primary species of PBM examined in this study was Hg(II), accounting for 78.6 ± 13.0 % (1σ , n = 9, Table S3) of total PBM.…”

“…A ternary system employing mass-dependent fractionation (MDF, reported as δ 202 Hg), the mass-independent fractionation (MIF) of odd isotopes (odd-MIF, reported as 199 Hg and 201 Hg), and the mass-independent fractionation of even isotopes (even-MIF, reported as 200 Hg) could offer diagnostic information on the source contributions and historical environmental processes of atmospheric Hg. In the troposphere, atmospheric Hg isotopes fractionate during mixing of plumes with various isotopic compositions and also during physical processes including volatilization from and dissolution to droplets (Estrade et al, 2009), diffusion (Koster van Groos et al, 2014), adsorption and desorption on the airborne particle surfaces (Fu et al, 2019a), and chemical processes (Blum et al, 2014). In addition, odd-MIF suggests the occurrence of photochemical processes when source mixing can be excluded (Bergquist and Blum, 2007); even-MIF signatures diagnose the contributions from wet precipitation in the natural environment (Enrico et al, 2016).…”

“…Several studies on atmospheric Hg isotopes were conducted at coastal areas, where as the receptors for mixing air plumes are from both continents and the MBL (Demers et al, 2015;Fu et al, 2018Fu et al, , 2019aRolison et al, 2013;Yu et al, 2016). These reported isotopic compositions in atmospheric Hg have been suggested as mixing results of continental anthropogenic emissions and the clean air from the MBL.…”