Atmospheric mercury (Hg) can be operationally defined into three types: gaseous elemental Hg (GEM), gaseous oxidized Hg (GOM), and particle-bound Hg (PBM). GEM is the most abundant Hg species in the global atmosphere (approximately 90%) and is well mixed due to its prolonged lifetime (0.5-1 year) and stable chemical properties. As GOM and PBM are more soluble in water than GEM and have a shorter lifetime (days to weeks), they are the predominant Hg species deposited to ecosystems through wet and dry deposition (Selin, 2009). The mutual transformations between these three Hg species have an important influence on the transportation and deposition of atmospheric Hg on a global scale (Schroeder & Munthe, 1998). The marine boundary layer (MBL) represents the atmospheric area affected by the oceanic surface, and its height significantly varies between middle-high latitudes (dozens to hundreds of meters) and low latitudes (up to 2000 m) (Hedgecock et al., 2005). The circulation of atmospheric Hg in the MBL differs from that in the planetary boundary layer (PBL) because of the significant differences in meteorological conditions and chemical compositions between the MBL and the PBL (e.g., humidity, sea salt aerosols, and oxidation mechanisms) (

Particle-bound mercury (PBM) records the oxidation of elemental mercury, of which the main oxidation pathways (Br•/Cl•/OH•/O 3 ) remain unclear, especially in the Southern Hemisphere. Here, we present latitudinal covariations of Hg and Sisotopic anomalies in cross-hemispheric marine aerosols that evidence an equator-to-poleward transition of Hg oxidants from OH•/O 3 in tropics to Br•/Cl• in polar regions highlighting thus the presence of distinct oxidation processes producing PBM. The correlations between Hg, S and O-isotopic compositions measured in PBM, sulfates and nitrates respectively within the aerosols highlight the implication of common oxidants in their formations at different latitudes. Our results open a new window to better quantify the present-day atmospheric Hg, S and N budgets and to evaluate the influences of aerosols on climate and ecosystems once the isotopic fractionations associated with each process have been determined.

Oceans play a key role in the global mercury (Hg) cycle, but studies on Hg isotopes in seawater are rare due to the extremely low Hg concentration and the lack of a good preconcentration method. Here, we introduce a new coprecipitation method for separating and preconcentrating Hg from seawater for accurate isotope measurement. The coprecipitation was achieved by sequential addition of 0.5 mL of 0.5 M CuSO 4 , 1 mL of 0.5 M Na 2 S, and 1 mL of 0.5 M CuSO 4 reagents, which allowed for quantitatively precipitating Hg from up to 10 L of seawater. The protocol was validated by testing synthetic solutions with varying Hg and iodide (I − ) concentrations and by comparing the reaction times of various reagents added. The method resulted in a quantitative recovery of 98 ± 12% (n = 32, two standard deviations, 2 SD) and a relatively low procedure blank (103 pg of Hg, n = 8). The precipitates were filtrated and analyzed for Hg isotopes. Repeated measurements of synthetic seawaters spiked with certificated standard materials (NIST 3133 and 3177) using the entire method gave identical Hg isotope ratios with near-quantitative Hg recovery, indicating no isotope fractionation during preconcentration. A total of six nearshore seawater samples from the Yellow Sea and the Bohai Sea (China) were analyzed using the coprecipitation method. The data showed a large fractionation of Hg isotopes and revealed the possible impact of both atmospheric and anthropogenic inputs to the coastal seawater Hg budget, implying the potential application of this method in studying marine Hg systematics and global Hg cycling.