Gaseous Mercury Research Articles

An Interhemispheric Difference in Atmospheric Gaseous Elemental Mercury Isotopes Reveals a New Insight in Oceanic Mercury Emissions

AbstractOceanic emission of gaseous elemental mercury (Hg0 or GEM) is an important source for atmospheric mercury (Hg), but existing estimates of global gross oceanic Hg0 emissions are highly variable (800–7,220 Mg yr−1). This study measured atmospheric GEM concentrations and isotopic compositions at two coastal sites in Terengganu, Malaysia, a region that receives air masses from both hemispheres, during 2019–2021 to diagnose the amount of oceanic Hg0 emissions. Significantly lower mean (±1sd) concentration (1.28 ± 0.20 ng m−3), Δ199Hg (−0.23 ± 0.03‰), and Δ200Hg (−0.066 ± 0.018‰) and significantly higher δ202Hg (0.43 ± 0.12‰) were observed during the wet season when air masses were predominantly from the Southern Hemisphere, compared with those (mean concentration, Δ199Hg, Δ200Hg, and δ202Hg of 1.77 ± 0.09 ng m−3, −0.17 ± 0.03‰, −0.045 ± 0.023‰, and 0.25 ± 0.11‰, respectively) during the dry season when air masses were predominantly from the Northern Hemisphere, suggesting interhemispheric difference in GEM concentrations and its isotopic compositions. Using a Δ200Hg mass balance model, we estimated that the oceanic Hg0 emissions from HgII reduction should be below 2,250 ± 891 Mg yr−1 (±1sd), which is at the low‐end range of the literature reported values. We then used the constrained value as emission input to a three‐dimensional atmospheric Hg isotope model and reproduced well the global distributions and interhemispheric gradient of atmospheric GEM Δ200Hg. The findings from the present study will help to better understand Hg0 emissions from global oceans and their roles in global atmospheric Hg cycling.

Comparative Foliar Atmospheric Mercury Accumulation across Functional Types in Temperate Trees.

Vegetation assimilation of atmospheric gaseous elemental mercury (GEM) represents the largest dry deposition pathway in global terrestrial ecosystems. This study investigated Hg accumulation mechanisms in deciduous broadleaves and evergreen needles, focusing on how ecophysiological strategies─reflected by δ13C, δ18O, leaf mass per area, and leaf dry matter content-mediated Hg accumulation. Results showed that deciduous leaves exhibited higher total Hg (THg) concentrations and accumulation rates (THgrate), which were 85.3 ± 17.7 and 110.0 ± 0.3% higher than those in evergreen needles. The two tree types exhibited distinct ecophysiological strategies: deciduous broadleaves, with higher stomatal conductance and photosynthetic rates, rapidly adjust stomata to changes in meteorological and pollutant factors, playing a key role in controlling THgrate. In contrast, evergreen needles featured stable stomatal control, highlighting the direct positive effect of GEM on their THgrate. Precipitation and wind speed negatively influenced foliar THgrate. Correlations between PM2.5, NO2, and THgrate in evergreen needles suggested synergistic patterns between atmospheric Hg and pollutants. This study underscores distinct GEM accumulation mechanisms across tree functional types and emphasizes the importance of species-specific foliar ecophysiological strategies. An empirical model linking THgrate with ecophysiological, meteorological, and atmospheric pollution factors was provided, contributing to the refinement of foliar Hg accumulation models.

Controlling morphology and doping tungsten to regulate sulfur species on molybdenum disulfide for removing Hg0 from flue gas

Molybdenum disulfide (MoS2) is considered a favorable absorbent for removing heavy metals. However, due to its various morphologies, MoS2 exhibits significant differences in its performance for removing mercury from flue gas. In the present study, the flower-like, spherical MoS2 and W-MoS2 were prepared by regulating the interlayer spacing and doping tungsten (W) in MoS2 for removing gaseous mercury (Hg0). The results show that the number of active sulfur sites (S2- and S2 2-) was critical to the adsorption performance of MoS2 for Hg0. The flower-like MoS2 demonstrated optimum properties below 125°C which attributed to the presence of dominated S2- sites, while spherical MoS2 and W-MoS2 showed a wider application temperature range (up to 175°C) during Hg0 removal which attributed to the unsaturated sulfur S2 2- and active oxygen. In terms of the mechanism, Hg0 is directly inserted into the Mo-S bond of MoS2 to form a transition state [Hg·Mo]-S, and then the original Mo-S is interrupted to form a new β-Hg-S bond, or combine with surface oxidation to form HgO. The oxygen in the flue gas can supplement the surface active oxygen on the MoS2, which enables the circulation of Mo5+. Hg0 also reacted with S2 2- to form α-HgS.

Mechanochemical Synthesis of ZnS-based Sepiolite Composites for Accommodation of Gaseous Mercury from Coal-Fired Flue Gas

Mechanochemical Synthesis of ZnS-based Sepiolite Composites for Accommodation of Gaseous Mercury from Coal-Fired Flue Gas

Long-Term Variation Characteristics and Health Risks of Atmospheric Hg in the Largest City in Northwestern China.

In this study, gaseous element mercury (GEM) and gaseous oxidized mercury (GOM) in the atmosphere were continuously observed at a minute resolution from 1 April 2019 to 31 December 2020 in urban Xi'an, the largest central city in Northwestern China. The concentrations of GEM and GOM drastically fluctuated within the ranges of 0.022-297 ng/m3 and 0.092-381 pg/m3, showing average values of 5.78 ± 7.36 ng/m3 and 14.2 ± 20.8 pg/m3, respectively. GEM and GOM showed a decreasing trend of 0.121 ng/m3 and 0.472 pg/m3 per month, respectively, which we believe was mainly caused by anthropogenic sources, especially by a reduction in coal-fired emissions, rather than meteorological factors. The significant positive correlation between GEM and PM2.5, SO2, NO2, and CO, as well as Cr, As, and Pb in PM2.5 also proves that. GEM showed a higher concentration at nighttime than daytime, while an M-shaped diurnal trend was observed for GOM. The hazard quotient of GEM for both males and females decreased at a rate of 0.003 per month, and children aged 2-5 were more sensitive to non-carcinogenic health risks. The changing trends, controlling factors, and human health risks of Hg in the atmosphere are necessary and crucial to study for improving our understanding of the impacts of Hg in Northwestern China.

Assessment of Incubation Experiments Using Isotopically Enriched Mercury Compounds in Seawater including Dissolved Gaseous Mercury

Assessment of Incubation Experiments Using Isotopically Enriched Mercury Compounds in Seawater including Dissolved Gaseous Mercury

Development of high-performance MoS2 with nanofoam architecture for gaseous elemental mercury sequestration: The key role of edge sulfur vacancy

Development of high-performance MoS2 with nanofoam architecture for gaseous elemental mercury sequestration: The key role of edge sulfur vacancy

Total gaseous mercury in Kathmandu, a South Asian metropolis: Temporal variations, sources apportionment and health risk assessment

South Asia is a global hotspot of air pollution gaining attention due to its severe implications, in which atmospheric mercury (Hg) could cause detrimental health effects in metropolitan areas. In this study, first-time year-round (January – December 2019) mean total gaseous mercury (TGM) concentration at Kathmandu, Nepal - a sub-tropical city in South Asia was reported at 9.9 ± 10.0 ng m-3. Seasonal TGM variation at Kathmandu showed highest concentration in winter (16.8 ± 16.9 ng m-3) and lowest in summer (2.9 ± 2.1 ng m-3). Generally higher daytime TGM concentration as opposed to night-time TGM indicated Hg build-up within atmospheric boundary layer due to low wind speed and high humidity. Events with high wind speed (> 30 m s-1) induced regional pollutant transport from nearby brick kilns and cement factories. Principal component analysis associated a major part of TGM with PM2.5 and CO and indicated the remarkable influence of fuel combustion and vehicular emissions. Backward trajectory and potential source contribution factor analysis further indicate the impact of regional Hg emissions and transboundary emissions from India towards Nepal, which expands beyond the Himalayas and the Tibetan Plateau. Prominent low-grade coal burning and kilning activities in winter spiked up TGM concentrations, resulting in the highest health quotient (HQ = 0.24) value, which could significantly impact public health. Our study presented the most comprehensive set of continuous annual atmospheric Hg monitoring data from Nepal in the South Asian region. The results serve as a baseline for regional atmospheric Hg levels and offer a critical reference for assessing and addressing air pollution concerns in Nepal as well as throughout South Asia.

Transport of Exogenous Anthropogenic Atmospheric Mercury to the Tibetan Plateau Identified Using Mercury Stable Isotopes

AbstractTransport of exogenous anthropogenic mercury (Hg) is an important source of Hg pollution in the Tibetan Plateau (TP) and its downstream water ecosystems, but the origins and contributions of Hg sources remain uncertain. Here, we investigate the concentrations and isotopic compositions of gaseous elemental mercury (GEM) at four rural sites in the TP and three urban sites surrounding the TP to quantify the sources of GEM in the TP. GEM concentrations in the surrounding cities (site‐specific means: 2.36–9.12 ng m−3) were highly elevated mainly due to strong local anthropogenic emissions as indicated by their negative δ202Hg and near zero Δ199Hg and Δ200Hg signatures. GEM isotopes indicate that GEM pollution in the TP, typically observed during the summer monsoon and the pre‐monsoon, were mainly caused by trans‐boundary transport of anthropogenic Hg from surroundings. Using an Hg isotope mixing model, we estimate that exogenous anthropogenic emissions on average contributed 26 ± 5% (1sd) to the GEM in the TP. Further analysis of the transport of anthropogenic Hg emissions based on the backward trajectory and gridded anthropogenic Hg emissions suggests that 16 ± 9% and 6 ± 13% of the GEM in the TP were derived from anthropogenic sources in South Asia and China, respectively. Our study suggests that anthropogenic Hg emissions in South Asia could be effectively transported to the TP across the Himalayan range. Future studies are needed to better assess the role of rapidly increasing anthropogenic Hg emissions in South Asia on the regional to global scale atmospheric Hg cycling.

Alternate materials for the capture and quantification of gaseous oxidized mercury in the atmosphere

Abstract. Methodologies for identifying atmospheric oxidized mercury (HgII) compounds, including particulate-bound HgII (HgII(p)) and gaseous oxidized mercury (HgII(g)), by mass spectrometry are currently under development. This method requires preconcentration of HgII for analysis due to high instrument detection limits relative to ambient HgII concentrations. The objective of this work was to identify and test materials for quantitative capture of HgII from the gas phase and to suggest potential surfaces onto which HgII can be collected, thermally desorbed, and characterized using mass spectrometry methods. From the literature, several compounds were identified as potential sorbent materials and tested in the laboratory for uptake of gaseous elemental mercury (Hg0) and HgII(g) (permeated from a HgBr2 salt source). Chitosan, α-Al2O3, and γ-Al2O3 demonstrated HgII(g) capture in ambient air laboratory tests, without sorbing Hg0 under the same conditions. When compared to cation exchange membranes (CEMs), chitosan captured a comparable quantity of HgII(g), while ≤90 % of loaded HgII(g) was recovered from α-Al2O3 and γ-Al2O3. When deployed in the field, the capture efficiency of chitosan decreased compared to CEMs, indicating that environmental conditions impacted the sorption efficiency of this material. The poor recovery of HgII from the tested materials compared to CEMs in the field indicates that further identification and exploration of alternative sorbent materials are required to advance atmospheric mercury chemistry analysis by mass spectrometry methods.

Predicting Behavior and Fate of Atmospheric Mercury in Soils: Age-Dating METAALICUS Hg Isotope Spikes with Fallout Radionuclide Chronometry.

Soils accumulate anthropogenic mercury (Hg) from atmospheric deposition to terrestrial ecosystems. However, possible reemission of gaseous elemental mercury (GEM) back to the atmosphere as well as downward migration of Hg with soil leachate influence soil sequestration of Hg in ways not sufficiently understood in global biogeochemical models. Here, we apply fallout radionuclide (FRN) chronometry to understand soil Hg dynamics by revisiting the METAALICUS experiments 20 years after enriched isotope tracers (198Hg, 200Hg, 201Hg, and 202Hg) were applied to two boreal watersheds in northwestern Ontario, Canada. Hg spikes formed well-defined peaks in organic horizons of both watersheds at depths of 3-6 cm and were accurately dated to the year of spike application in 6 of 7 cases (error = -0.8 ± 1.2 years). A seventh site was depleted by ca. 90% of both the 200Hg spike and background Hg, and the spike was dated 16 years older than its application. Robust FRN age models and mass balances demonstrate that loss of Hg is attributable to its specific physicochemical behavior at this site, but more work is required to attribute this to reemission or leaching. This study demonstrates the potential of FRN chronometry to provide insights into Hg accumulation, mobilization, and fate in forest soils.

Promoting elemental mercury immobilization performance from smelting flue gas over a wide temperature range via cobalt-doped copper sulfide adsorbents

Copper sulfide (CuS) sorbent exhibits great potential for gaseous elemental mercury (Hg0) decontamination, but it still suffers from a narrow operating temperature. Therefore, designing advanced CuS sorbents that have a high activity level for capturing Hg0 and thermal stability at a high temperature range is challenging. Herein, we propose a metal doping strategy to fabricate a bimetallic sulfide adsorbent. Benefiting the unique structure and composition, a mesoporous structure and an abundance of unsaturated sulfur sites ensure that CuxCo(1–x)Sy provides a desirable level of adsorption for Hg0. The experimental results indicate the optimum Co doping mass concentration of 5 %. The Cu0.95Co0.05Sy not only performs satisfactory Hg0 adsorption at elevated temperatures (Hg0 average adsorption efficiency of over 97.3 %, Hg0 average adsorption rate of over 2.7 μg/g/min), but also presents an exciting regeneration and recycle performance (a Hg0 adsorption efficiency of over 94 % after 10 cycles). The adsorption capacity of Cu0.95Co0.05Sy at the breakthrough threshold of 25 % reaches 5.22 mg/g, surpassing most of metal sulfide sorbents for Hg0 immobilization at 150 °C. As far as Hg0 adsorption is concerned, the composition of typical smelting flue gases has almost no effect. According to further studies, unsaturated coordination short-chain sulfur (S22−) sites are essential for adsorption of Hg0 and are capable of directly forming α-HgS from Hg0. In both the contrast experiment and density functional theory calculations, the cobalt doping strategy enhances the thermal stability of the active S22− ligand and the Hg0 adsorption properties. This study not only provide a prospective adsorbent for Hg0 sequestration at wide temperature range, but also explores a method of utilizing gaseous contaminants for resource utilization.

Unexpected anthropogenic emission decreases explain recent atmospheric mercury concentration declines.

Anthropogenic activities emit ~2,000 Mg y-1 of the toxic pollutant mercury (Hg) into the atmosphere, leading to long-range transport and deposition to remote ecosystems. Global anthropogenic emission inventories report increases in Northern Hemispheric (NH) Hg emissions during the last three decades, in contradiction with the observed decline in atmospheric Hg concentrations at NH measurement stations. Many factors can obscure the link between anthropogenic emissions and atmospheric Hg concentrations, including trends in the reemissions of previously released anthropogenic ("legacy") Hg, atmospheric sink variability, and spatial heterogeneity of monitoring data. Here, we assess the observed trends in gaseous elemental mercury (Hg0) in the NH and apply biogeochemical box modeling and chemical transport modeling to understand the trend drivers. Using linear mixed effects modeling of observational data from 51 stations, we find negative Hg0 trends in most NH regions, with an overall trend for 2005 to 2020 of -0.011 ± 0.006 ng m-3 y-1 (±2 SD). In contrast to existing emission inventories, our modeling analysis suggests that annual NH anthropogenic emissions must have declined by at least 140 Mg between the years 2005 and 2020 to be consistent with observed trends. Faster declines in 95th percentile Hg0 values than median values in Europe, North America, and East Asian measurement stations corroborate that the likely cause is a decline in nearby anthropogenic emissions rather than background legacy reemissions. Our results are relevant for evaluating the effectiveness of the Minamata Convention on Mercury, demonstrating that existing emission inventories are incompatible with the observed Hg0 declines.

Unraveling atmospheric mercury dynamics at Mauna Loa through the isotopic analysis of total gaseous mercury

Our investigation seeks to uncover the intricate nature of mercury dynamics in the free troposphere through analysis of the isotopic composition of total gaseous elemental mercury (TGM) at the high altitude Mauna Loa Observatory (MLO, 3397 m) in Hawaii, USA. By focusing on this unique site, we aim to provide essential insights into the behavior and cycling of mercury, contributing valuable data to a deeper understanding of its global distribution and environmental impacts. Forty-eight hours of TGM sampling from January to September 2022 revealed significant variations in δ202Hg (−1.86 % to −0.32 %; mean = −1.17 ± 0.65 %, 2 SD, n = 34) and small variations in Δ199Hg (−0.27 % to 0.04 %; mean = −0.13 ± 0.14 %, 2 SD, n = 34) and Δ200Hg (−0.20 % to 0.06 %; mean = −0.05 ± 0.13 %, 2 SD, n = 34). During the sampling period, GEM was negatively correlated with gaseous oxidized mercury (GOM). However, the GOM/GEM ratio was not −1, suggesting that GEM oxidation and subsequent scavenging occurred previously. The δ202Hg isotopic compositions of TGM at MLO were different from those of reported values of high-altitude mountains; the δ202Hg of TGM at MLO was lower than the isotopic ratios that were obtained from other mountain regions. The unique atmospheric conditions at Mauna Loa, with (upslope winds during the day and downslope winds at night, likely result in the) possibly mixing of GEMs from terrestrial (and possibly oceanic GEM emission) sources with and tropospheric sources, influencing and affect the isotopic composition. During the late summer to early fall (September 14–28), negative correlations were found between relative humidity and GOM and between particle number concentrations and Δ199Hg, indicating the gas-to-particle partitioning of the atmospheric mercury during this period. This study will improve our understanding on mercury dynamics of marine origin and high altitudes and shed light on its complex interactions with environmental factors.

Atmospheric Mercury Concentrations and Isotopic Compositions Impacted by Typical Anthropogenic Mercury Emissions Sources.

Coal-fired power plants (CFPPs) and cement plants (CPs) are important anthropogenic mercury (Hg) emission sources. Mercury speciation profiles in flue gas are different among these sources, leading to significant variations in local atmospheric Hg deposition. To quantify the impacts of Hg emissions from CFPPs and CPs on local-scale atmospheric Hg deposition, this study determined concentrations and isotopes of ambient gaseous elemental mercury (GEM), particulate-bound mercury (PBM), and precipitation total Hg (THg) at multiple locations with different distances away from a CFPP and a CP. Higher concentrations of GEM and precipitation THg in the CFPP area in summer were caused by higher Hg emission from the CFPP, resulting from higher electricity demand. Higher concentrations of GEM, PBM, and precipitation THg in the CP area in winter compared to those in summer were related to the higher output of cement. Atmospheric Hg concentration peaked near the CFPP and CP and decreased with distance from the plants. Elevated GEM concentration in the CFPP area was due to flue gas Hg0 emissions, and high PBM and precipitation Hg concentrations in the CP area were attributed to divalent Hg emissions. It was estimated that Hg emissions from the CFPP contributed 58.3 ± 20.9 and 52.3 ± 25.9% to local GEM and PBM, respectively, and those from the CP contributed 47.0 ± 16.7 and 60.0 ± 25.9% to local GEM and PBM, respectively. This study demonstrates that speciated Hg from anthropogenic emissions posed distinct impacts on the local atmospheric Hg cycle, indicating that Hg speciation profiles from these sources should be considered for evaluating the effectiveness of emission reduction policies. This study also highlights the Hg isotope as a useful tool for monitoring environmental Hg emissions.

Tree Rings Mercury Controlled by Atmospheric Gaseous Elemental Mercury and Tree Physiology.

Tree rings are an emerging atmospheric mercury (Hg) archive. Questions have arisen, though, regarding their mechanistic controls and reliability. Here, we report contrasting tree-ring Hg records in three collocated conifer species: Norway spruce (Picea abies), Scots pine (Pinus sylvestris), and European larch (Larix decidua), which are from a remote boreal forest. Centennial atmospheric Hg trends at the site, derived from varved lake sediments, peats, and atmospheric monitoring, indicated a steady rise from the 1800s, peaking in the 1970s, and then declining. Prior to ca. 2005, larch and spruce tree rings reproduced the peak in the atmospheric Hg trend, while pine tree rings peaked in the 1930s, likely due to the prolonged sapwood period and ambiguity in the heartwood-sapwood boundary of pine. Since ca. 2005, tree rings from all species showed increasing Hg concentrations in the physiologically active outer rings despite declining atmospheric Hg concentrations. The good agreement between Hg and nitrogen concentrations in active tree-ring cells indicates a similar transport mechanism and cautions against their applicability as atmospheric Hg archives. Our results suggest that tree-ring Hg records are controlled by atmospheric Hg and tree physiology. We provide recommendations for using tree-ring Hg archives that take tree physiology into account.

Temporal Evolution of Gaseous Mercury Across the Sea Ice‐Seawater Interface: A Mesocosm Study

AbstractIn the marine cryosphere, seasonal sea ice dynamics affect the behavior of gaseous mercury, yet the mechanism remains poorly understood. By carrying out an outdoor sea ice mesocosm study, we examine primarily the abiotic factors influencing mercury dynamics and show distinct behaviors of gaseous mercury across the sea ice‐seawater interface over the full growth‐melt cycle. The distribution of gaseous mercury in sea ice is influenced by entrapment of gaseous mercury from different sources into sea ice of different textures, transport schemes within sea ice, and in situ cryo‐processes that affect mercury speciation. In the growing sea ice sections where solar radiation penetrated, production of gaseous mercury was observed, supporting the occurrence of in‐ice cryo‐photoreduction of divalent mercury. In under‐ice seawater, concentrations of dissolved gaseous mercury decreased gradually during ice growth and increased rapidly to pre‐freezing levels as ice started to melt, suggesting that the atmosphere‐sea ice‐seawater exchange pathway of gaseous mercury could be re‐established through melting first‐year sea ice. Our results from this unique mesocosm study provide new insights on the dynamics of gaseous mercury in and around sea ice that are primarily driven by abiotic processes, assisting model parameterizations for mercury cycling in polar regions.

Atmospheric mercury species at Nam Co (4730m a.s.l.), a highland background site in the inland Tibetan Plateau: implications of mercury potential sources.

A field survey was conducted in the central Tibetan Plateau (Nam Co) in China for high-time resolution measurements of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM). Average concentrations (± 1 SD) of GEM, PBM, and GOM from November 2014 to March 2015 were 1.11 ± 0.20ngm-3, 50.8 ± 26.5pgm-3, and 3.6 ± 3.2pgm-3, respectively. During the monitoring period, both GEM and GOM exhibited relative stability in their monthly variations, whereas PBM concentrations were significantly higher in winter compared to those in later autumn and early spring. In terms of diurnal variations, the maximum concentration of GEM was typically observed after sunrise, while PBM reached its peak before sunrise, and the highest concentration of GOM was recorded in the afternoon. Vertical convection conditions, photochemical production, and gas-particle partitioning were responsible for the diurnal cycle of atmospheric mercury. Based on modeling results, it was determined that the air mass transported from South Asia significantly impacted atmospheric mercury levels at Nam Co Station. The regions of western and central Nepal, central and eastern Pakistan, and northern India were identified as potential sources of atmospheric mercury at Nam Co.

The Deep Removal of Mercury in Contaminated Acid by Colloidal Agglomeration Materials M201

The high-temperature roasting/smelting process of copper and zinc concentrates will cause the mercury in the concentrate to evaporate into the flue gas, and most of the mercury in the flue gas will eventually enter the waste acid in its ionic form. A highly efficient mercury removal agent M201 with long carbon chains and loaded active functional groups can adsorb and disperse fine particles for mercury removal in the system. Through bridging, the linear structure is woven into a network to achieve large-scale capture and dispersion of fine particles and colloidal substances. The recommended operating conditions for developing mercury deep purification technology are as follows: M201 reagent concentration of 50 g/L, 6 mL/L added acid solution, room temperature, mixing time of 5 min, air flotation time of 10 min, ventilation rate of 0.1 L/min, H2SO4 concentration of 33.67 g/L, and the residual mercury content of 2 mg/L (the mercury content reaches 0.01 mg/L after two-stage mercury removal treatment). Meanwhile, the residual arsenic content is 21.9 mg/L. This study shows a better separation of arsenic and mercury and achieves one-step mercury removal.

Combating air pollution significantly reduced air mercury concentrations in China.

In the past decade, China has motivated proactive emission control measures that have successfully reduced emissions of many air pollutants. For atmospheric mercury, which is a globally transported neurotoxin, much less is known about the long-term changes in its concentrations and anthropogenic emissions in China. In this study, over a decade of continuous observations at four Chinese sites show that gaseous elemental mercury (GEM) concentrations continuously increased until the early 2010s, followed by significant declines at rates of 1.8%-6.1% yr-1 until 2022. The GEM decline from 2013 to 2022 (by 38.6%±12.7%) coincided with the decreasing concentrations of criteria air pollutants in China and were larger than those observed elsewhere in the northern hemisphere (5.7%-14.2%). The co-benefits of emission control measures contributed to the reduced anthropogenic Hg emissions and led to the GEM decline in China. We estimated that anthropogenic GEM emissions in China were reduced by 38%-50% (116-151 tons) from 2013 to 2022 using the machine-learning and relationship models.