An assessment of variations in mercury deposition to Antarctica over the past 34,000 years

We performed a comparison analysis of the variations .in Mercury ( Hg) concentrations and the precipitation proxies ( e. g. , 18 O values and 10 Be concentrations) in the Dome C ice core. The results showed that there were significant correlations between Hg and δ 10O values, 10Be concentrations, indicating that the accumulation rate in Dome C is one of the key factors controlling the variations of Hg concentrations in the past 34 ,000 years, and implying that Hg concentrations in ice core can be used as another reliable proxy of precipitation rate in Antarctica. Based upon the high-resolution δ 18O values, we estimated the variations in mercury deposition flux to Antarctica over the past 34,000 years. The highest mercury deposition flux is about 3. 80 pg cm-2 yr-1 during the Last Glacial Maxium (LGM) as high as 3. 5 times of the mercury deposition flux ( about 1. 08 pg cm -2 yr -1) in Holocene due to the fluctuations in natural mercury emissions such as the oceanic biological emissions.

A simulation study of mercury release fluxes from soils in wet–dry rotation environment

A simulative mesocosm study was conducted to evaluate the influence of wet-dry rotation on mercury（Hg） flux from soil/water to air and the distribution of Hg species in water as well as Hg chemical fractions in soil. Three types of soil were employed including two kinds of paddy soil, Typic Purpli-Udic Cambosols（TPUC） and Xanthi-Udic Ferralosols（XUF）, as well as the Alluvial Soil（AS） from Three Gorge reservoir area in Chongqing, China. The results showed that Hg fluxes in wetting periods were significantly higher than that in drying periods. It might be due to the formation of a layer of stable air over the water surface in which some redox reactions promote evasion processes over the water surface. This result indicated that more Hg would be evaporated from the Three Gorge reservoir and paddy soil field during the flooding season. Hg fluxes were positively correlated with air temperature and solar irradiation, while negatively correlated with air humidity and the electronic conductivity of water. Hg fluxes from AS and TPUC were significantly higher than that from XUF, which might be due to the higher organic matter（OM） contents in XUF than TPUC and AS. The reduction processes of oxidized Hg were restrained due to the strong binding of Hg to OM, resulting in the decrease in Hg flux from the soil.

The soil displacement measurement of mercury emission flux of the sewage irrigation farmlands in Northern China

Mercury fate of sewage irrigation in farmlands deserves attention with increasing scarcity of freshwater resources for agriculture in the worldwide.Soil-air total gaseous mercury(TGM)fluxes from four-sewage and one-fresh water irrigated farmlands were determined simultaneously.During maize-wheat rotation,soil-air TGM fluxes showed patterns of both emission and deposition during different growth stages.It enhanced one-order of magnitude emission with increased Hg contamination from historical sewage irrigation.A linear response relationship of TGM fluxes with soil Hg concentration was found,which showed greater TGM emission potential comparing with those from forest and urban soils.However,the ratio of soil-air TGM flux in daytime to nighttime were 3.94 in maize-season and 3.41 in wheat-season,respectively,which were little related to the change in soil Hg concentration.Furthermore,soil temperature and moisture,ambient-air TGM concentration all effected TGM evasion from sewage-irrigated soils.The data presented here suggest that evasion of TGMfromhistorical sewage irrigation farmlands with high Hg concentrations may be potential hotspots for Hg emission in atmosphere,and it was likely to underestimate Hg emissions from farmlands in existing emissions inventory.Additional regionalinvestigations and process-level researches are needed to better understand role of sewage irrigation farmlands in local-global Hg-biogeochemical-cycles.

Improved atmospheric mercury simulation using updated gas-particle partition and organic aerosol concentrations

The gaseous or particulate forms of divalent mercury(HgⅡ) significantly impact the spatial distribution of atmospheric mercury concentration and deposition flux(FLX). In the new nested-grid GEOS-Chem model, we try to modify the HgⅡ gas-particle partitioning relationship with synchronous and hourly observations at four sites in China. Observations of gaseous oxidized Hg(GOM), particulate-bound Hg(PBM), and PM 2.5 were used to derive an empirical gas-particle partitioning coefficient as a function of temperature( T) and organic aerosol(OA) concentrations under different relative humidity(RH). Results showed that with increasing RH, the dominant process of HgⅡ gas-particle partitioning changed from physical adsorption to chemical desorption. And the dominant factor of HgⅡ gas-particle partitioning changed from T to OA concentrations. We thus improved the simulated OA concentration field by introducing intermediate-volatility and semi-volatile organic compounds(I/SVOCs) emission inventory into the model framework and refining the volatile distributions of I/SVOCs according to new filed tests in the recent literatures. Finally, normalized mean biases(NMBs) of monthly gaseous element mercury(GEM), GOM, PBM, WFLX were reduced from-33%–29%, 95%–300%, 64%–261%, 117%–122% to-13%–0%,-20%–80%,-31%–50%,-17%–23%. The improved model explains 69%–98% of the observed atmospheric Hg decrease during 2013–2020 and can serve as a useful tool to evaluate the effectiveness of the Minamata Convention on Mercury.