Gaseous Mercury Research Articles

Gaseous mercury capture using seaweed biochars modified by clean ultraviolet/hydrogen peroxide advanced oxidation process

Seaweed-based biochars stemmed from the solid wastes of seaweed-based biomass pyrolysis were used to reduce the emission of elemental mercury. An environmentally-friendly ultraviolet/hydrogen peroxide advanced oxidation process modification method was used to increase the active species over seaweed-based biochars for elemental mercury adsorption. Results suggest that the elemental mercury capture performance of seaweed-based biochars is greatly improved after the ultraviolet/hydrogen peroxide advanced oxidation process modification. The optimum adsorption temperature and hydrogen peroxide concentration are 120 °C and 4%, respectively. The characterization results display that the clean ultraviolet/hydrogen peroxide advanced oxidation process modification greatly enhances the rising of oxygen functional group on seaweed-based biochars surface. In particular, the presence of CO and COOH/COOC groups is conducive to Hg0 capture. The process of elemental mercury capture over the tested seaweed-based biochars accords with pseudo-second-order adsorption kinetic equation. Chemical sorption is the pivotal controlling link of the whole mercury capture process. The preparation costs of Sargassum-based biochar and Enteromorpha-based biochar are lower than that of chitosan adsorbent and commercial AC. In addition, the modified seaweed biochars have good regeneration performance, which is conducive to greatly reducing the cost of mercury removal. This research can provide new inspiration for the green modification of biochar and the development of clean mercury removal adsorbent.

Copper selenide sensitized low-cost porous coordination polymers towards efficient capture trace gaseous elemental mercury

Mercury, as a highly toxic atmospheric pollutant, poses serious hazards to global health and ecosystems. Developing low-cost sorbents with simultaneous fast capture rate and large uptake capacity to reduce elemental mercury (Hg0) emissions from industrial flue gas remains a formidable challenge. Herein, a rationally designed surfactant-assisted method was developed to construct copper selenide (CuSe) sensitized porous coordination polymers (CAU-10-H) as an efficient Hg remediator. The CuSe/CAU-10-H (0.8NC-CAU) exhibits superior near-100 % gaseous Hg0 removal efficiency over a wide temperature range (30–120 °C), implying its adaptability under different implementations. The equilibrium Hg0 adsorption capacity and initial Hg0 uptake rate of 0.8NC-CAU are 748.09 mg·g−1 and 63.21 μg·g−1·min−1, respectively, surpassing that of conventional sorbents and comparable to the benchmark materials. Furthermore, 0.8NC-CAU can adapt to harsh conditions with different flue gas impurities containing SO2, NO, and H2O to maintain high selectivity and stability, which is advantageous for real-world applications. Density functional theory (DFT) reveals that unsaturated selenium ligands as electron acceptors are critical affinity sites for facilitating Hg0 capture, resulting in stable HgSe species. More importantly, the facile preparation, prominent uptake capacity, and rapid capture rate of the 0.8NC-CAU material make it cost-effective. This work proposes a potential trap for Hg0 capture from industrial flue gas and facilitates the development of hybrid-functionalized materials for environmental remediation.

Chemodynamics of Mercury (Hg) in a Southern Reservoir Lake (Cane Creek Lake, Cookeville, TN, USA): I—Estimation of the Kinetics of Photochemical Reduction of Aquatic Hg(II) Using Field-Measured Data of Hg Water/Air Exchange and Dissolved Gaseous Hg

An alternative, independent estimation of the kinetics of aquatic Hg(II) photochemical reduction featuring dissolved gaseous mercury (DGM) emission from water in consideration was obtained by using a mass balance box model. An interactive Excel spreadsheet was constructed to implement the model equations to yield the rate constants and the rates of the Hg(II) photoreduction. The model calculations used field-measured data of DGM paired with its emission flux coupled with the corresponding field sampling times. This data set came from a previous, separate, year-long field study conducted at a southern reservoir lake (Cane Creek Lake, Cookeville, Putnam County, TN). The mean value of the model-calculated rate constants (kDGM) of the Hg(II) photoreduction for the warm season (June–August) (4.5 fM h−1/pg L−1) is higher than that for the cold season (October–January) (2.2 fM h−1/pg L−1). The rate constants were found to be the highest (22.5 fM h−1/pg L−1) in August whereas the lowest (0.03 fM h−1/pg L−1) in January. The model-calculated rate constants are clearly higher in value than but comparable in order of magnitude to the published kinetic data. The model-calculated rates (rDGM) of the Hg(II) photoreduction are significantly higher, by one order of magnitude (102 vs. 101) than the apparent rates calculated using the same field DGM data without consideration of the Hg emission from the water. A sensitivity analysis of the model parameters points to a high sensitivity of Hg emission flux to the rate constant under modeled realistic environmental conditions. The initial Hg(II) concentration is also a sensitive model parameter under certain conditions. The results of our model study support the conclusion that DGM emission from water has a strong impact on the kinetics of aquatic Hg(II) photoreduction and the model calculation can provide an independent, valuable approach for estimating the kinetics of aquatic Hg(II) photoreduction.

Probing the limits of sampling gaseous elemental mercury passively in the remote atmosphere

Deployment times of at least two months and dedicated efforts to limit contamination during transport and storage are recommended to obtain reliable results when using passive samplers for gaseous elemental mercury in the remote atmosphere.

Spontaneous adsorption–oxidation of gaseous elemental mercury via a conjugated unit –NH+˙–Cl*: creation and mechanisms

A Cl-doped protonated polyaniline-coated multiwall carbon nanotube (Cl-PANI+@MWCNT) composite provides a new method for the spontaneous adsorption–oxidation of gaseous elemental mercury.

Observed in-plume gaseous elemental mercury depletion suggests significant mercury scavenging by volcanic aerosols

We observed complete GEM depletion in a volcanic plume.

Removal of gaseous elemental mercury using corn stalk biochars modified by a green oxidation technology

Straw biochars are the widely used carbon materials for adsorbing gaseous Hg0 due to developed porous structure. However, its application is restricted by scarcity of active sites on carbon surface. Existing modification methods such as acids, halides, sulfides, metal oxides, etc. have problem of secondary pollution. In this work, a corn stalk biochar modified with UV/H2O2 green modification technology was prepared to capture gaseous Hg0 for the first time. The physicochemical properties of the adsorbent and the effect of several key parameters containing H2O2 concentration, adsorption temperatures and common gas components on gaseous Hg0 capture were studied. The kinetic process and mechanisms of gaseous Hg0 adsorption were also expounded. Research indicated that through producing ·OH free radicals with high activity, UV/H2O2 green modification technology could not only improve pore structure of corn stalk biochar, but also make containing-O functional group more abundant on carbon surface, promoting gaseous Hg0 adsorption. Optimal H2O2 modification concentration and adsorption temperature are 3 wt% and 120 °C, respectively. The capture process of gaseous Hg0 accorded with quasi second-order kinetic equation. Chemisorbed oxygen (O*) and CO functional group show pivotal roles in the capture processes of gaseous Hg0.

Gaseous elemental mercury (GEM) exchange flux from soil-vegetation to atmosphere at a meadow steppe

Gaseous elemental mercury (GEM) exchange flux from soil-vegetation to atmosphere at a meadow steppe

Long-range transport of atmospheric speciated mercury from the eastern waters of Taiwan Island to northern South China Sea

This study explored the temporospatial distribution, gas-particle partition, and pollution sources of atmospheric speciated mercury (ASM) from the eastern offshore waters of the Taiwan Island (TI) to the northern South China Sea (SCS). Both gaseous and particulate mercury were simultaneously sampled at three remote sites in four seasons. The average concentrations of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate bound mercury (PBM) were 2.05 ± 0.45 ng/m3, 19.17 ± 5.39 pg/m3, and 0.11 ± 0.06 ng/m3, respectively. The concentrations of GEM and PBM in the cold seasons were higher than those in the warm seasons, but those of GOM had an opposite trend. In terms of gas-solid partition, ASM was apportioned as 91.3–97.3% of GEM and 2.7–8.7% of GOM and PBM. The average concentrations of GEM, GOM, and PBM at the Green Island (GI) were 2.21 ± 0.47 ng/m3, 22.31 ± 5.35 pg/m3, and 0.12 ± 0.06 ng/m3; those at the Kenting Peninsula (KT) were 2.11 ± 0.43 ng/m3, 20.57 ± 4.38 pg/m3, and 0.11 ± 0.06 ng/m3; and those at the Dongsha Islands (DS) were 1.84 ± 0.40 ng/m3, 15.19 ± 3.58 pg/m3, and 0.08 ± 0.05 ng/m3, respectively. Overall, the spatial distribution of ASM concentrations showed the order as: GI > KT > DS. Air masses blown mainly from the West Pacific Ocean (WPO) and SCS in summer showed the lowest ASM concentrations. Oppositely, high ASM concentrations were commonly observed in spring and winter when polluted air masses were blown by Asian Northeastern Monsoons (ANMs). The transport routes of polluted air masses were originated mainly from North China, Central China, Northeast China, Korea and Japan, and mostly passed through the urban and industrial regions in the northeastern Asian countries.

Gaseous mercury evasion from bare and grass-covered soils contaminated by mining and ore roasting (Isonzo River alluvial plain, Northeastern Italy)

High amounts of mercury (Hg) can be released into the atmosphere from soil surfaces of legacy contaminated areas as gaseous elemental mercury (Hg0). The alluvial plain of the Isonzo River (NE Italy) suffered widespread Hg contamination due to the re-distribution of Hg-enriched material discharged by historical cinnabar mining at the Idrija mine (Slovenia), but an assessment of Hg0 releases from the soils of this area is still lacking. In this work, Hg0 fluxes at the soil-air interface were evaluated using a non-steady state flux chamber coupled with a real-time Hg0 analyser at 6 sites within the Isonzo River plain. Measurements were performed in summer, autumn, and winter both on bare and grass-covered soil plots at regular time intervals during the diurnal period. Moreover, topsoils were analysed for organic matter content and Hg total concentration and speciation. Overall, Hg0 fluxes tracked the incident UV radiation during the sampling periods with daily averages significantly higher in summer (62.4 ± 14.5–800.2 ± 178.8 ng m−2 h−1) than autumn (15.2 ± 4.7–280.8 ± 75.6 ng m−2 h−1) and winter (16.9 ± 7.9–187.8 ± 62.7 ng m−2 h−1) due to higher irradiation and temperature, which favoured Hg reduction reactions. In summer and autumn significant correlations were observed between Hg0 fluxes and soil Hg content (78–95% cinnabar), whereas this relationship was not observed in winter likely due to relatively low emissions found in morning measurements in all sites coupled with low temperatures. Finally, vegetation cover effectively reduced Hg0 releases in summer (∼9–68%) and autumn (∼41–78%), whereas the difference between fluxes from vegetated and bare soils was not evident during winter dormancy due to scarce soil shading. These results suggest the opportunity of more extended spatial monitoring of Hg0 fluxes particularly in the croplands covering most of the Isonzo River alluvial plain and where bare soils are frequently disturbed by agricultural practices and directly exposed to radiation.

Enhanced natural releases of mercury in response to the reduction in anthropogenic emissions during the COVID-19 lockdown by explainable machine learning

Abstract. The wide spread of the coronavirus (COVID-19) has significantly impacted the global human activities. Compared to numerous studies on conventional air pollutants, atmospheric mercury that has matched sources from both anthropogenic and natural emissions is rarely investigated. At a regional site in eastern China, an intensive measurement was performed, showing obvious decreases in gaseous elemental mercury (GEM) during the COVID-19 lockdown, while it was not as significant as most of the other measured air pollutants. Before the lockdown, when anthropogenic emissions dominated, GEM showed no correlation with temperature and negative correlations with wind speed and the height of the boundary layer. In contrast, GEM showed significant correlation with temperature, while the relationship between GEM and the wind speed/boundary layer disappeared during the lockdown, suggesting the enhanced natural emissions of mercury. By applying a machine learning model and the SHAP (SHapley Additive exPlanations) approach, it was found that the mercury pollution episodes before the lockdown were driven by anthropogenic sources, while they were mainly driven by natural sources during and after the lockdown. Source apportionment results showed that the absolute contribution of natural surface emissions to GEM unexpectedly increased (44 %) during the lockdown. Throughout the whole study period, a significant negative correlation was observed between the absolute contribution of natural and anthropogenic sources to GEM. We conclude that the natural release of mercury could be stimulated to compensate for the significantly reduced anthropogenic GEM via the surface–air exchange in the balance of mercury.

A Review of Dry Deposition Schemes for Speciated Atmospheric Mercury

This study reviewed the existing framework of dry deposition schemes for speciated atmospheric mercury. As the most commonly used methods for mercury dry deposition estimation, the big-leaf resistance scheme for gaseous oxidized mercury (GOM), the size distribution regarded resistance scheme for particulate bound mercury (PBM), and the bidirectional air-surface exchange scheme for gaseous elemental mercury (GEM) were introduced in detail. Sensitivity analysis were conducted to quantitatively identify the key parameters for the estimation of speciated mercury dry deposition velocities. The dry deposition velocity of GOM was found to be sensitive to the wind speed and some land use related parameters. The chemical forms of GOM could have a significant impact on the dry deposition velocity. The dry deposition velocity of PBM is sensitive to the mass fraction of PBM in coarse particles, while that of GEM is most sensitive to air temperature. Future research needs were proposed accordingly.

Enhanced adsorption of gaseous mercury on activated carbon by a novel clean modification method

Activated carbon is the most widely used gaseous mercury adsorbent. However, lack of active sites on its surface leads to its poor mercury adsorption ability. Various modification methods, including acid-alkali, sulfide, halogenide, metallic oxides, etc., are used to modify activated carbon to enhance its adsorption ability, but there are still secondary pollution or/and solid waste problems. This article tried to use a clean ultraviolet (UV)/H2O2 advanced oxidation process (AOP) to modify activated carbon by generating hydroxyl radicals for enhancing adsorption of Hg0 on activated carbon. The activated carbon modification parameters, main influencing factors, mechanism and kinetics of mercury removal were studied. Studies indicate that UV/H2O2 AOP modification could substantively enhance the Hg0 adsorption over activated carbon. The optimum H2O2 modification concentration is 9%, and the optimum reaction temperature for Hg0 adsorption is 120 °C. The optimized Hg0 adsorption capacity reaches 3636.43 μg/g. Characterization measurement (e.g., BET, SEM, FTIR, XPS, etc.) demonstrates that UV/H2O2 AOP modification has slight destructive effect on pore structure of activated carbon, but significantly raises the contents of oxygen-containing functional groups (e.g., -OH, CO and CO). It is found that Hg0 adsorption is enhanced by O2 and NO in gas stream, while is inhibited by H2O and SO2 in gas stream. The whole process of Hg0 adsorption is mainly dominated via chemical adsorption step, and the oxygen-containing functional groups (e.g., -OH, CO and CO) and the chemisorbed oxygen (O*) are the main active sites to realize the oxidative removal of Hg0 on the modified activated carbon surface.

Gaseous mercury capture using Bi2S3 nanorods decorated ZSM-5 with superior sulfur resistance

Zeolite ZSM-5, as a crystalline microporous material, has attracted widespread interest in diverse research areas because of its big specific surface area, high thermal stability, and shape selectivity. Here, xBi2S3/ZSM-5 compounds is easily synthesized using a molten salt method and employed to capture elemental mercury in the temperature range of 60–260°C. Pristine ZSM-5 displays a weak Hg0 adsorption capability. Bi2S3 decoration can greatly reinforce the mercury adsorption capability of ZSM-5 due to addition of active sulfide species. 20Bi2S3/ZSM-5 with 20 wt% Bi2S3 loading value performs optimally toward Hg° capture associated with a mercury removing efficiency of 90.8–96.5% within 100–140°C. In addition, 20Bi2S3/ZSM-5 is nearly impervious to NO and SO2 with respect to mercury removal. One-dimensional nanorod structure of Bi2S3 and big specific surface area of ZSM-5 probably account for the superior mercury capture performance of xBi2S3/ZSM-5 compounds.

Measuring and Regression Modeling of Gas–Particle Partitioning of Atmospheric Oxidized Mercury at a Coastal Site in Shanghai

Gas–particle partitioning between reactive gaseous mercury (RGM) and particle bound mercury (PBM) controls the fates of atmospheric oxidized mercury (namely reactive mercury, RM). We conducted a long-term observations of gaseous elemental mercury (GEM), RGM, PBM, and auxiliary parameters in Chongming Island, Shanghai, China, to understand the characteristics of speciated mercury and their gas–particle partitioning behaviors. The entire average abundances of GEM, RGM and PBM were 2.12 ± 0.94 ng/m3, 14.75 ± 9.94 pg/m3 and 21.81 ± 30.46 pg/m3, respectively. An observation data dependent empirical gas–particle partitioning relationship of partitioning coefficient and temperature log(1/KP) = −2692.20/T + 10.57 was obtained, and it varied in different season being by the temperature. To further evaluate the influences of temperature, particulate matter (PM), relative humidity on RGM and PBM partitioning process, the particulate fraction (φ = PBM/(PBM + RGM)) was used in this study. High φ values (φ > 0.8) mainly occurred at low temperature domain (<281 K), and high PM concentration enhanced this influence. In addition, high relative humidity shifts RGM from atmosphere partitioning to PBM in response to the diurnal valley φ values at 13:00–16:00 in the summer. Photochemical reactions were proposed to play important roles on partitioning processes between RGM and PBM. This study will benefit for the understanding of oxidized mercury fate and influencing factors in the complex atmospheric pollutants.

Mercury photoreduction and photooxidation kinetics in estuarine water: Effects of salinity and dissolved organic matter

Net photoreduction of divalent mercury (Hg(II)) and volatilization of photoreduction products (i.e., elemental mercury (Hg(0))/dissolved gaseous mercury (DGM)) is a mechanism by which mercury burdens in ecosystems are lessened. The effects of salinity on mercury photoreactions were investigated while controlling the concentration of DOM (>1 kDa) using natural surface water from the tidal Jijuktu'kwejk (Cornwallis River) and processed with a tangential ultrafiltration-dilution technique. Pseudo first-order rate constants in estuarine water salinity dilutions ranged between 0.22 h−1 and 0.73 h−1. The amount of mercury available for photoreduction (Hg(II)RED) ranged between 67.2 and 265.9 pg. Pseudo first-order rate constants decreased with increasing salinity treatments (0–13.5 g L−1), with minimal change in rate constants occurring in higher salinity treatments (e.g. 20.3 or 26.8 g L−1), while Hg(II)RED increased with salinity. In lower salinity treatments, DOM was more photoactive. Taken together, results suggest changes in the mercury photoreduction mechanism from DOM-bound electron transfer to photochemically produced secondary reduction products with increasing salinity. Experiments examining photooxidation showed decreases in Hg (0) with longer exposure time, suggesting transformation of Hg(II)RED into a non-reducible form. This research highlights the importance of salinity and DOM interactions in estuarine surface water and their effects on mercury photochemistry.

Primary Measurement of Gaseous Elemental Mercury Concentration with a Dynamic Range of Six Decades.

We present a primary method for absolute reference material-free measurement of gaseous elemental mercury mass concentration based on laser absorption spectroscopy at wavelengths near 254 nm and anchored to the international system of units. A 76 m-long multipass cell provides a detection limit of 1 ng m-3 for an averaging time of 8 min. A dual-cell arrangement, comprising a single-pass and a multipass cell, provides a dynamic range of six decades and spans from ambient to emission levels of gaseous elemental mercury (1 ng m-3 to 1000 μg m-3). The relative standard uncertainty of the measurement is 0.5% in the 0.25 to 1000 μg m-3 range.

Empirical Model of Gaseous Mercury Emissions for the Analysis of Working Conditions in Outdoor Highly Contaminated Sites

The project SUBproducts4LIFE is a LIFE-funded research project that aims to demonstrate innovative circular economy concepts by repurposing industrial subproducts/waste (coal ash and gypsum from coal power plants, blast furnace slag, and steelmaking slag from steel factories) for the remediation of contaminated soils and brownfield areas associated with Hg mining on a large scale. Within the project, one of the objectives is related to worker safety by developing protocols and elaborating a guide of good practices to work under in these highly contaminated areas. The present research aims to assess the working conditions in an abandoned mine facility in terms of gaseous mercury in the environment, evaluating the main areas of the mine to ensure the health and safety of all workers and visitors. The study developed an empirical model for estimating the gaseous mercury concentration at any temperature with the target of scheduling the work to avoid occupational hazards. The research concluded that working without restrictions for temperatures under 15 °C in all the mine’s facilities is possible.

Gaseous elemental mercury and its evasion fluxes in the marine boundary layer of the marginal seas of the northwestern Pacific: Results from two cruises in September–December 2019

There are many questions regarding the behavior of mercury in the sea-atmosphere system of the northwestern Pacific. Continuous underway measurements of atmospheric gaseous elemental mercury (GEM) and measurements of sea-air GEM evasion fluxes were carried out in the marginal seas of northwestern Pacific from the South China Sea to the Sea of Okhotsk in fall-winter 2019. The median GEM concentration (1.1 ng/m3) was lower than both the background value and the averages previously observed in these areas. A latitudinal gradient of atmospheric GEM and GEM evasion fluxes with maximum values at southern latitudes was found. The following areas have been identified as potential source areas: the Kurill area of the Pacific Ocean Northeast China, Korean Peninsula, and the territory from the southwest coast of the Yellow Sea to the south of Indochina. Seasonal variations were observed in the Sea of Japan and East China Sea with higher GEM concentrations in winter than in fall. Our data and analysis of published data showed significant relationships between GEM evasion fluxes, latitude and sea surface temperature (SST). It seems that on a global scale, along with the GEM gradient between water and atmosphere, SST is the most significant parameter for sea-air GEM evasion fluxes.

Dynamics, distribution, and transformations of mercury species from pyrenean high-altitude lakes

While mercury (Hg) is a major concern in all aquatic environments because of its methylation and biomagnification pathways, very few studies consider Hg cycling in remote alpine lakes which are sensitive ecosystems. Nineteen high-altitude pristine lakes from Western/Central Pyrenees were investigated on both northern (France) and southern (Spain) slopes (1620–2600 m asl.). Subsurface water samples were collected in June 2017/2018/2019 and October 2017/2018 for Hg speciation analysis of inorganic mercury (iHg(II)), monomethylmercury (MMHg), and dissolved gaseous mercury (DGM) to investigate spatial and seasonal variations. In June 2018/2019 and October 2018, more comprehensive studies were performed in four lakes by taking water column depth profiles. Besides, in-situ incubation experiments using isotopically enriched Hg species (199iHg(II), 201MMHg) were conducted to investigate Hg transformation mechanisms in the water column. While iHg(II) (0.08–1.10 ng L−1 in filtered samples; 0.11–1.19 ng L−1 in unfiltered samples) did not show significant seasonal variations in the subsurface water samples, MMHg (<0.03–0.035 ng L−1 in filtered samples; <0.03–0.062 ng L−1 in unfiltered samples) was significantly higher in October 2018, mainly because of in-situ methylation. DGM (0.02–0.68 ng L−1) varies strongly and can exhibit higher levels in comparison with other pristine areas. Depth profiles and incubation experiments highlighted the importance of in-situ biotic methylation triggered by anoxic conditions in bottom waters. In-situ incubations confirm that significant methylation, demethylation and photoreduction extents are taking place in the water columns. Overall, drastic environmental changes occurring daily and seasonally in alpine lakes are providing conditions that can both promote Hg methylation (stratified anoxic waters) and MMHg photodemethylation (intense UV light). In addition, light induced photoreduction is a major pathway controlling significant gaseous Hg evasion. Global warming and potential eutrophication may thus have direct implications on Hg turnover and MMHg burden in those remote ecosystems.