Oxidation of elemental Hg in anthropogenic and marine airmasses

Abstract. Mercury (Hg) is a neurotoxin that bioaccumulates in the food chain. Mercury is emitted to the atmosphere primarily in its elemental form, which has a long lifetime allowing global transport. It is known that atmospheric oxidation of gaseous elemental mercury (GEM) generates reactive gaseous mercury (RGM) which plays an important role in the atmospheric mercury cycle by enhancing the rate of mercury deposition to ecosystems. However, the primary GEM oxidants, and the chemical composition of RGM are poorly known. Using speciated mercury measurements conducted at the Mt. Bachelor Observatory since 2005 we present two previously unidentified sources of RGM to the free troposphere (FT). Firstly, we observed elevated RGM concentrations, large RGM/GEM-ratios, and anti-correlation between RGM and GEM during Asian long-rang transport events, demonstrating that RGM is formed from GEM by in-situ oxidation in some anthropogenic pollution plumes in the FT. During the Asian pollution events the measured RGM/GEM-enhancement ratios reached peak values, up to ~0.20, which are significantly larger than ratios typically measured (RGM/GEM < 0.03) in the Asian source region. Secondly, we observed very high RGM levels – the highest reported in the FT – in clean air masses that were processed upwind of Mt. Bachelor Observatory over the Pacific Ocean. The high RGM concentrations (up to 700 pg m−3), high RGM/GEM-ratios (up to 1), and very low ozone levels during these events provide observational evidence indicating significant GEM oxidation in the lower FT in some conditions.

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Two new sources of reactive gaseous mercury in the free troposphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-29203-2012 ◽

2012 ◽

Vol 12 (11) ◽

pp. 29203-29233 ◽

Cited By ~ 2

Author(s):

H. Timonen ◽

J. L. Ambrose ◽

D. A. Jaffe

Keyword(s):

Source Region ◽

Elemental Mercury ◽

Anthropogenic Pollution ◽

Atmospheric Mercury ◽

Free Troposphere ◽

Mercury Deposition ◽

Gaseous Elemental Mercury ◽

Reactive Gaseous Mercury ◽

Gaseous Mercury ◽

The Pacific

Abstract. Mercury (Hg) is a neurotoxin that bioaccumulates in the food chain. Mercury is emitted to the atmosphere primarily in its elemental form, which has a long lifetime allowing global transport. It is known that atmospheric oxidation of gaseous elemental mercury (GEM) generates reactive gaseous mercury (RGM) which plays an important role in the atmospheric mercury cycle by enhancing the rate of mercury deposition to ecosystems. However, the primary GEM oxidants, and the sources and chemical composition of RGM are poorly known. Using speciated mercury measurements conducted at the Mt. Bachelor Observatory since 2005 we present two previously unidentified sources of RGM to the free troposphere (FT). Firstly, we observed elevated RGM concentrations, large RGM/GEM-ratios, and anti-correlation between RGM and GEM during Asian long-rang transport events, demonstrating that RGM is formed from GEM by in-situ oxidation in some anthropogenic pollution plumes in the FT. During the Asian pollution events the measured RGM/GEM-ratios reached peak values, up to ~0.20, which are significantly larger than ratios typically measured (RGM/GEM < 0.05) in the Asian source region. Secondly, we observed very high RGM levels – the highest reported in the FT – in clean air masses that were processed upwind of Mt. Bachelor Observatory over the Pacific Ocean. The high RGM concentrations (up to 700 pg m−3), high RGM/GEM-ratios (up to 1), and very low ozone levels during these events provide the first observational evidence indicating significant GEM oxidation in the lower FT. The identification of these processes changes our conceptual understanding of the formation and distribution of oxidized Hg in the global atmosphere.

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Gaseous mercury in coastal urban areas

Environmental Chemistry ◽

10.1071/en10088 ◽

2010 ◽

Vol 7 (6) ◽

pp. 537 ◽

Cited By ~ 3

Author(s):

Anne L. Soerensen ◽

Henrik Skov ◽

Matthew S. Johnson ◽

Marianne Glasius

Keyword(s):

Urban Areas ◽

Marine Boundary Layer ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

Mercury Deposition ◽

Mercury Emissions ◽

Gaseous Elemental Mercury ◽

Gaseous Mercury ◽

Range Transport ◽

Aquatic Food

Environmental context Mercury is a neurotoxin that bioaccumulates in the aquatic food web. Atmospheric emissions from urban areas close to the coast could cause increased local mercury deposition to the ocean. Our study adds important new data to the current limited knowledge on atmospheric mercury emissions and dynamics in coastal urban areas. Abstract Approximately 50% of primary atmospheric mercury emissions are anthropogenic, resulting from e.g. emission hotspots in urban areas. Emissions from urban areas close to the coast are of interest because they could increase deposition loads to nearby coastal waters as well as contribute to long range transport of mercury. We present results from measurements of gaseous elemental mercury (GEM) and reactive gaseous mercury (RGM) in 15 coastal cities and their surrounding marine boundary layer (MBL). An increase of 15–90% in GEM concentration in coastal urban areas was observed compared with the remote MBL. Strong RGM enhancements were only found in two cities. In urban areas with statistically significant GEM/CO enhancement ratios, slopes between 0.0020 and 0.0087 ng m–3 ppb–1 were observed, which is consistent with other observations of anthropogenic enhancement. The emission ratios were used to estimate GEM emissions from the areas. A closer examination of data from Sydney (Australia), the coast of Chile, and Valparaiso region (Chile) in the southern hemisphere, is presented.

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Observation and analysis of speciated atmospheric mercury in Shangri-la, Tibetan Plateau, China

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-11041-2014 ◽

2014 ◽

Vol 14 (8) ◽

pp. 11041-11074 ◽

Cited By ~ 2

Author(s):

H. Zhang ◽

X. W. Fu ◽

C.-J. Lin ◽

X. Wang ◽

X. B. Feng

Keyword(s):

Tibetan Plateau ◽

Atmospheric Transport ◽

Seasonal Pattern ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

North India ◽

Air Masses ◽

Gaseous Elemental Mercury ◽

Wet Scavenging ◽

In The Beginning

Abstract. This study reports the speciated concentration and the potential sources of atmospheric mercury measured at the Shangri-La Atmosphere Watch Regional Station (SAWRS), a pristine high-altitude site (3580 m a.s.l.) in Tibetan Plateau, China. The total gaseous mercury (TGM, defined as the sum of Gaseous Elemental Mercury, GEM, and gaseous oxidized mercury, GOM), GOM and particulate-bound mercury (PBM) were monitored from November 2009 to November 2010 to investigate the characteristics and atmospheric transport of mercury influenced by the Indian summer monsoon (ISM) and westerlies. The mean concentrations of TGM, PBM and GOM were 2.55 ± 0.73 ng m−3, 37.78 ± 31.35 pg m−3 and 7.90 ± 7.89 ng m−3. A notable seasonal pattern was observed with higher TGM concentrations in the beginning and end of the ISM. High TGM concentrations were associated with the transport of dry air that carried regional anthropogenic emissions from both domestic and foreign sources. The low PBM and GOM level was attributed to the deposition and wet scavenging during the ISM period. Backward trajectory analysis of air masses associated with TGM levels suggested that both the ISM and westerlies can carry Hg emitted in Burma, Bengal bay and north India to the SAWRS.

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Atmospheric mercury over sea ice during the OASIS-2009 campaign

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-7007-2013 ◽

2013 ◽

Vol 13 (14) ◽

pp. 7007-7021 ◽

Cited By ~ 27

Author(s):

A. Steffen ◽

J. Bottenheim ◽

A. Cole ◽

T. A. Douglas ◽

R. Ebinghaus ◽

...

Keyword(s):

Sea Ice ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

The Arctic ◽

Mercury Deposition ◽

International Polar Year ◽

Bromine Oxide ◽

Gaseous Elemental Mercury ◽

Significant Difference ◽

Mercury Cycle

Abstract. Measurements of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (PHg) were collected on the Beaufort Sea ice near Barrow, Alaska, in March 2009 as part of the Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) and OASIS-Canada International Polar Year programmes. These results represent the first atmospheric mercury speciation measurements collected on the sea ice. Concentrations of PHg averaged 393.5 pg m−3 (range 47.1–900.1 pg m−3) and RGM concentrations averaged 30.1 pg m−3 (range 3.5–105.4 pg m−3) during the two-week-long study. The mean concentration of GEM during the study was 0.59 ng m−3 (range 0.01–1.51 ng m−3) and was depleted compared to annual Arctic ambient boundary layer concentrations. It is shown that when ozone (O3) and bromine oxide (BrO) chemistry were active there is a positive linear relationship between GEM and O3, a negative one between PHg and O3, a positive correlation between RGM and BrO, and none between RGM and O3. For the first time, GEM was measured simultaneously over the tundra and the sea ice. The results show a significant difference in the magnitude of the emission of GEM from the two locations, with significantly higher emission over the tundra. Elevated chloride levels in snow over sea ice are proposed to be the cause of lower GEM emissions over the sea ice because chloride has been shown to suppress photoreduction processes of RGM to GEM in snow. Since the snowpack on sea ice retains more mercury than inland snow, current models of the Arctic mercury cycle may greatly underestimate atmospheric deposition fluxes because they are based predominantly on land-based measurements. Land-based measurements of atmospheric mercury deposition may also underestimate the impacts of sea ice changes on the mercury cycle in the Arctic. The predicted changes in sea ice conditions and a more saline future snowpack in the Arctic could enhance retention of atmospherically deposited mercury and increase the amount of mercury entering the Arctic Ocean and coastal ecosystems.

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Previously unaccounted atmospheric mercury deposition in a midlatitude deciduous forest

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2105477118 ◽

2021 ◽

Vol 118 (29) ◽

pp. e2105477118

Author(s):

Daniel Obrist ◽

Eric M. Roy ◽

Jamie L. Harrison ◽

Charlotte F. Kwong ◽

J. William Munger ◽

...

Keyword(s):

Deciduous Forest ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

Aquatic Biota ◽

Carbon Dioxide Assimilation ◽

Mercury Deposition ◽

Gaseous Elemental Mercury ◽

Photosynthetic Carbon ◽

Proxy Measure ◽

High Mercury

Mercury is toxic to wildlife and humans, and forests are thought to be a globally important sink for gaseous elemental mercury (GEM) deposition from the atmosphere. Yet there are currently no annual GEM deposition measurements over rural forests. Here we present measurements of ecosystem–atmosphere GEM exchange using tower-based micrometeorological methods in a midlatitude hardwood forest. We measured an annual GEM deposition of 25.1 µg ⋅ m−2 (95% CI: 23.2 to 26.7 1 µg ⋅ m−2), which is five times larger than wet deposition of mercury from the atmosphere. Our observed annual GEM deposition accounts for 76% of total atmospheric mercury deposition and also is three times greater than litterfall mercury deposition, which has previously been used as a proxy measure for GEM deposition in forests. Plant GEM uptake is the dominant driver for ecosystem GEM deposition based on seasonal and diel dynamics that show the forest GEM sink to be largest during active vegetation growing periods and middays, analogous to photosynthetic carbon dioxide assimilation. Soils and litter on the forest floor are additional GEM sinks throughout the year. Our study suggests that mercury loading to this forest was underestimated by a factor of about two and that global forests may constitute a much larger global GEM sink than currently proposed. The larger than anticipated forest GEM sink may explain the high mercury loads observed in soils across rural forests, which impair water quality and aquatic biota via watershed Hg export.

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Method development estimating ambient oxidized mercury concentration from monitored mercury wet deposition

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-11287-2013 ◽

2013 ◽

Vol 13 (22) ◽

pp. 11287-11293 ◽

Cited By ~ 3

Author(s):

S. Chen ◽

X. Qiu ◽

L. Zhang ◽

F. Yang ◽

P. Blanchard

Keyword(s):

Distribution Function ◽

Beta Distribution ◽

Wet Deposition ◽

Method Development ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

Mercury Deposition ◽

Gaseous Elemental Mercury ◽

Spatial Coverage ◽

Beta Distribution Function

Abstract. To quantify mercury dry deposition, the Atmospheric Mercury Network (AMNet) of the National Atmospheric Deposition Program (NADP) was established recently to monitor the speciated atmospheric mercury (i.e. gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particulate-bound mercury (PBM)). However, the spatial coverage of AMNet is far less than the long-established Mercury Deposition Network (MDN) for wet deposition monitoring. The present study describes the first attempt linking ambient concentration of the oxidized mercury (GOM + PBM) with wet deposition aiming to estimate GOM + PBM roughly at locations and/or times where such measurement is not available but where wet deposition is monitored. The beta distribution function is used to describe the distribution of GOM + PBM and is used to predict GOM + PBM from monitored wet deposition. The mean, median, mode, standard deviation, and skewness of the fitted beta distribution parameters were generated using data collected in 2009 at multiple monitoring superstations. The established beta distribution function from the 2009 GOM + PBM data is used to construct a model that predicts GOM + PBM from wet deposition data. The model is validated using 2010 data at multiple stations, and the predicted monthly GOM + PBM concentrations agree reasonably well with measurements. The model has many potential applications after further improvements and validation using different data sets.

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Speciated atmospheric mercury at Waliguan Global Atmospheric Watch station in the northeastern Tibetan Plateau: implication of dust related sources for particulate bound mercury

10.5194/acp-2021-290 ◽

2021 ◽

Author(s):

Hui Zhang ◽

Xuewu Fu ◽

Ben Yu ◽

Baoxin Li ◽

Peng Liu ◽

...

Keyword(s):

Tibetan Plateau ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

Dust Particles ◽

Anthropogenic Emissions ◽

The Tibetan Plateau ◽

Mean Values ◽

Air Masses ◽

Gaseous Elemental Mercury ◽

Aerosol Index

Abstract. To understand the ambient levels and sources of atmospheric mercury (Hg) in the Tibetan Plateau, a full-year continuous measurement of speciated atmospheric mercury was conducted at Waliguan (WLG) Baseline Observatory (3816 m a.s.l.) from May 2012 to April 2013. Mean concentrations (±1 SD) of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particulate bound mercury (PBM) during the whole study period were 1.90 ± 0.80 ng m−3, 12.0 ± 10.6 pg m−3 and 65.4 ± 63.2 pg m−3, respectively. Seasonal variations of GEM were very small, while those of PBM were quite large with mean values being four times higher in cold (102.3 ± 66.7 pg m−3) than warm (22.8 ± 14.6 pg m−3) season. Anthropogenic emissions to the east of Tibetan Plateau contributed significantly to GEM pollution at WLG, while dust particles originated from desert and Gobi regions in Xinjiang province and Tibetan Plateau to the west of WLG were responsible to PBM pollution at WLG. This finding is also supported by the significant positive correlation between daily PBM concentration and daily cumulative absorbing aerosol index (AAI) encountered by air masses transported during the preceding two days.

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Global deposition of speciated atmospheric mercury to terrestrial surfaces: an overview

10.5194/acp-2019-347 ◽

2019 ◽

Author(s):

Lei Zhang ◽

Peisheng Zhou ◽

Shuzhen Cao ◽

Yu Zhao

Keyword(s):

Dry Deposition ◽

Urban Areas ◽

Wet Deposition ◽

Current Knowledge ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

Future Research ◽

Observation System ◽

Mercury Deposition ◽

Gaseous Elemental Mercury

Abstract. One of the most important processes in the global mercury biogeochemical cycling is the deposition of atmospheric mercury, including gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM), to terrestrial surfaces. In this paper, methods for the observation of wet, dry, litterfall, throughfall, and cloud/fog deposition and models for mercury dry deposition are reviewed. Surrogate surface methods with cation exchange membranes are widely used for GOM dry deposition measurements, while observation methods for GEM dry deposition are more diverse. The methodology for Hg wet deposition is more mature, but the influence of cloud/fog scavenging is easy to neglect. Dry deposition models for speciated mercury have high uncertainties owing to the presence of sensitive parameters related to GOM chemical forms. Observation networks for mercury wet deposition have been developed worldwide, with the Global Mercury Observation System (GMOS) covering the northern hemisphere, the tropics, and the southern hemisphere. Wet deposition implies the spatial distribution of atmospheric mercury pollution, while GOM dry deposition depends highly on the elevation. Litterfall Hg deposition is crucial to forests. Urban areas have high wet deposition and PBM dry deposition because of high reactive mercury levels. Grasslands and forests have significant GOM and GEM dry deposition, respectively. Evergreen broadleaf forests bear high litterfall Hg deposition. Future research needs have been proposed based on the current knowledge of global mercury deposition to terrestrial surfaces.

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Monsoon-facilitated characteristics and transport of atmospheric mercury at a high-altitude background site in southwestern China

10.5194/acp-2016-506 ◽

2016 ◽

Cited By ~ 2

Author(s):

Hui Zhang ◽

Xuewu Fu ◽

Che-Jen Lin ◽

Lihai Shang ◽

Yiping Zhang ◽

...

Keyword(s):

Southeast Asia ◽

Summer Monsoon ◽

Source Region ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

Southwestern China ◽

Anthropogenic Source ◽

Strong Impact ◽

Gaseous Elemental Mercury ◽

South And Southeast Asia

Abstract. To better understand the influence of monsoonal climate and transport of atmospheric mercury (Hg) in southwestern China, measurements of total gaseous mercury (TGM, defined as the sum of gaseous elemental mercury, GEM, and gaseous oxidized mercury, GOM), particulate bound mercury (PBM) and GOM were carried out at Ailaoshan Station (ALS, 2450 m a.s.l.) in southwestern China from May 2011 to May 2012. The mean concentrations (± standard deviation) for TGM, GOM and PBM were 2.09 ± 0.63 ng m−3, 2.2 ± 2.3 pg m−3 and 31.3 ± 28.4 pg m−3, respectively. TGM showed a monsoonal distribution pattern with relatively higher concentrations (p = 0.021) during the Indian summer monsoon (ISM, from May to September) and the East Asia summer monsoon (EASM, from May to September) periods than that in the non-ISM period. Similarly, GOM and PBM concentrations were higher in the ISM period than in the non-ISM period. This study suggests that the ISM and the EASM have a strong impact on long-range and transboundary transport of Hg between southwestern China and South and Southeast Asia. Several high TGM events were accompanied by the occurrence of northern wind during the ISM period, indicating anthropogenic Hg emissions from inland China could rapidly increase TGM levels at ALS due to strengthening of the EASM. Most of the TGM and PBM events occurred at ALS during the non-ISM period. Meanwhile, high CO concentrations were also observed at ALS, indicating that a strong south tributary of westerlies could have transported Hg from South and Southeast Asia to southwestern China during the non-ISM period. Consequently, southwestern China is an important anthropogenic source region of ALS during the ISM period. The biomass burning in Southeast Asia and anthropogenic Hg emissions from South Asia should be the source of atmospheric Hg in remote areas of southwestern China during the non-ISM period.

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Multi-year record of atmospheric mercury at Dumo d’Urville, East Antarctic coast: continental outflow and oceanic influences

10.5194/acp-2016-257 ◽

2016 ◽

Author(s):

Hélène Angot ◽

Iris Dion ◽

Nicolas Vogel ◽

Michel Legrand ◽

Olivier Magand ◽

...

Keyword(s):

Elemental Mercury ◽

Atmospheric Mercury ◽

Observation System ◽

Daily Maximum ◽

Air Masses ◽

Gaseous Elemental Mercury ◽

Antarctic Plateau ◽

Continental Scale ◽

Surface Snow ◽

Snow Samples

Abstract. Under the framework of the Global Mercury Observation System (GMOS) project, a 3.5-year record of atmospheric gaseous elemental mercury (Hg(0)) has been gathered at Dumont d’Urville (DDU, 66°40’S, 140°01’E, 43 m above sea level) on the East Antarctic coast. Additionally, surface snow samples were collected in February 2009 during a traverse between Concordia Station located on the East Antarctic plateau and DDU. The record of atmospheric Hg(0) at DDU reveals particularities that are not seen at other coastal sites: a gradual decrease of concentrations over the course of winter, and a daily maximum concentration around midday in summer. Additionally, total mercury concentrations in surface snow samples were particularly elevated near DDU (up to 194.4 ng L−1) as compared to measurements at other coastal Antarctic sites. These differences can be explained by the more frequent arrival of inland air masses at DDU than at other coastal sites. This confirms the influence of processes observed on the Antarctic plateau on the cycle of atmospheric mercury at a continental scale, especially in areas subject to recurrent katabatic winds. DDU is also influenced by oceanic air masses and our data suggest that the ocean plays a dual role on Hg(0) concentrations. The open ocean may represent a source of atmospheric Hg(0) in summer whereas the sea-ice surface may provide reactive halogens in spring that can oxidize Hg(0).

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