Previously unaccounted atmospheric mercury deposition in a midlatitude deciduous forest

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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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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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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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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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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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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Oxidation of elemental Hg in anthropogenic and marine airmasses

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-2827-2013 ◽

2013 ◽

Vol 13 (5) ◽

pp. 2827-2836 ◽

Cited By ~ 43

Author(s):

H. Timonen ◽

J. L. Ambrose ◽

D. A. Jaffe

Keyword(s):

Source Region ◽

Elemental Mercury ◽

Anthropogenic Pollution ◽

Atmospheric Mercury ◽

Mercury Deposition ◽

Air Masses ◽

Gaseous Elemental Mercury ◽

The Pacific ◽

Global Transport ◽

Clean Air

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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Simulation of atmospheric mercury depletion events (AMDEs) during polar springtime using the MECCA box model

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-7165-2008 ◽

2008 ◽

Vol 8 (23) ◽

pp. 7165-7180 ◽

Cited By ~ 35

Author(s):

Z.-Q. Xie ◽

R. Sander ◽

U. Pöschl ◽

F. Slemr

Keyword(s):

Aqueous Phase ◽

Ozone Depletion ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

Box Model ◽

Rate Coefficients ◽

Mercury Species ◽

Phase Reaction ◽

Gaseous Elemental Mercury ◽

Sea Salt Aerosol

Abstract. Atmospheric mercury depletion events (AMDEs) during polar springtime are closely correlated with bromine-catalyzed tropospheric ozone depletion events (ODEs). To study gas- and aqueous-phase reaction kinetics and speciation of mercury during AMDEs, we have included mercury chemistry into the box model MECCA (Module Efficiently Calculating the Chemistry of the Atmosphere), which enables dynamic simulation of bromine activation and ODEs. We found that the reaction of Hg with Br atoms dominates the loss of gaseous elemental mercury (GEM). To explain the experimentally observed synchronous depletion of GEM and O3, the reaction rate of Hg+BrO has to be much lower than that of Hg+Br. The synchronicity is best reproduced with rate coefficients at the lower limit of the literature values for both reactions, i.e. kHg+Br≈3×10−13 and kHg+BrO≤1×10−15 cm3 molecule−1 s−1, respectively. Throughout the simulated AMDEs, BrHgOBr was the most abundant reactive mercury species, both in the gas phase and in the aqueous phase. The aqueous-phase concentrations of BrHgOBr, HgBr2, and HgCl2 were several orders of magnitude larger than that of Hg(SO3)22−. Considering chlorine chemistry outside depletion events (i.e. without bromine activation), the concentration of total divalent mercury in sea-salt aerosol particles (mostly HgCl42−) was much higher than in dilute aqueous droplets (mostly Hg(SO3)22−), and did not exhibit a diurnal cycle (no correlation with HO2 radicals).

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Speciated Atmospheric Mercury during Haze and Non-haze Days in an Inland City in China

10.5194/acp-2016-467 ◽

2016 ◽

Author(s):

Qianqian Hong ◽

Zhouqing Xie ◽

Cheng Liu ◽

Feiyue Wang ◽

Pinhua Xie ◽

...

Keyword(s):

Elemental Mercury ◽

Atmospheric Mercury ◽

Central China ◽

Mercury Emissions ◽

Gaseous Elemental Mercury ◽

Enhanced Production ◽

Mercury Transport ◽

Haze Pollution ◽

The Mean ◽

Haze Days

Abstract. Long-term continuous measurements of speciated atmospheric mercury were conducted at Hefei, a mid-latitude inland city in east central China, from July 2013 to June 2014. The mean concentrations (± standard deviation) of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle-bound mercury (PBM) were 3.95 ± 1.93 ng m−3, 2.49 ± 2.41 pg m−3 and 23.3 ± 90.8 pg m−3, respectively, during non-haze days, and 4.74 ± 1.62 ng m−3, 4.32 ± 8.36 pg m−3 and 60.2 ± 131.4 pg m−3, respectively, during haze days. Potential source contribution function (PSCF) analysis suggested that the atmospheric mercury pollution during haze days was caused primarily by local mercury emissions, instead of via long-range mercury transport. In addition, the disadvantageous diffussion during haze days will also enhance the level of atmospheric mercury. Compared to the GEM and RGM, change in PBM was more sensitive to the haze pollution. The mean PBM concentration during haze days was 2.5 times that during non-haze days due to elevated concentrations of particulate matter. A remarkable seasonal trend in PBM was observed with concentration decreasing in the following order in response to the frequency of haze days: autumn, winter, spring, summer. A distinct diurnal relationship was found between GEM and RGM during haze days, with the peak values of RGM coinciding with the decline in GEM. Using HgOH as an intermediate product during GEM oxidation, our results suggest that NO2 aggregation with HgOH could explain the enhanced production of RGM during the daytime in haze days. Increasing level of NOx will potentially accelerate the oxidation of GEM despite the decrease of solar radiation.

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A synthesis of atmospheric mercury depletion event chemistry linking atmosphere, snow and water

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-10837-2007 ◽

2007 ◽

Vol 7 (4) ◽

pp. 10837-10931 ◽

Cited By ~ 19

Author(s):

A. Steffen ◽

T. Douglas ◽

M. Amyot ◽

P. Ariya ◽

K. Aspmo ◽

...

Keyword(s):

Sea Ice ◽

Current Knowledge ◽

Kinetic Studies ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

The Arctic ◽

Polar Regions ◽

Environmental Media ◽

Gaseous Elemental Mercury ◽

History Of

Abstract. It was discovered in 1995 that, during the spring time, unexpectedly low concentrations of gaseous elemental mercury (GEM) occurred in the Arctic air. This was surprising for a pollutant known to have a long residence time in the atmosphere; however conditions appeared to exist in the Arctic that promoted this depletion of mercury (Hg). This phenomenon is termed atmospheric mercury depletion events (AMDEs) and its discovery has revolutionized our understanding of the cycling of Hg in Polar Regions while stimulating a significant amount of research to understand its impact to this fragile ecosystem. Shortly after the discovery was made in Canada, AMDEs were confirmed to occur throughout the Arctic, sub-Artic and Antarctic coasts. It is now known that, through a series of photochemically initiated reactions involving halogens, GEM is converted to a more reactive species and is subsequently associated to particles in the air and/or deposited to the polar environment. AMDEs are a means by which Hg is transferred from the atmosphere to the environment that was previously unknown. In this article we review the history of Hg in Polar Regions, the methods used to collect Hg in different environmental media, research results of the current understanding of AMDEs from field, laboratory and modeling work, how Hg cycles around the environment after AMDEs, gaps in our current knowledge and the future impacts that AMDEs may have on polar environments. The research presented has shown that while considerable improvements in methodology to measure Hg have been made the main limitation remains knowing the speciation of Hg in the various media. The processes that drive AMDEs and how they occur are discussed. As well, the roles that the snow pack, oceans, fresh water and the sea ice play in the cycling of Hg are presented. It has been found that deposition of Hg from AMDEs occurs at marine coasts and not far inland and that a fraction of the deposited Hg does not remain in the same form in the snow. Kinetic studies undertaken have demonstrated that bromine is the major oxidant depleting Hg in the atmosphere. Modeling results demonstrate that there is a significant deposition of Hg to Polar Regions as a result of AMDEs. Models have also shown that Hg is readily transported to the Arctic from source regions, at times during springtime when this environment is actively transforming Hg from the atmosphere to the snow and ice surfaces. The presence of significant amounts of methyl Hg in snow in the Arctic surrounding AMDEs is important because this species is the link between the environment and impacts to wildlife and humans. Further, much work on methylation and demethylation processes have occurred but are not yet fully understood. Recent changes in the climate and sea ice cover in Polar Regions are likely to have strong effects on the cycling of Hg in this environment; however more research is needed to understand Hg processes in order to formulate meaningful predictions of these changes. Mercury, Atmospheric mercury depletion events (AMDE), Polar, Arctic, Antarctic, Ice

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Measurement-based modeling of daytime and nighttime oxidation of atmospheric mercury

10.5194/acp-2017-39 ◽

2017 ◽

Cited By ~ 2

Author(s):

Maor Gabay ◽

Mordechai Peleg ◽

Erick Fredj ◽

Eran Tas

Keyword(s):

Lower Limit ◽

Rate Constant ◽

Field Measurements ◽

Elemental Mercury ◽

Chemical Oxidation ◽

Atmospheric Mercury ◽

Gaseous Elemental Mercury ◽

Measurement Results ◽

Kinetic Calculations ◽

First Time

Abstract. Accurate characterization of gaseous elemental mercury (GEM) chemical oxidation pathways and their kinetics is critically important for assessing the transfer of atmospheric mercury to bioaquatic systems. Recent comprehensive field measurements have suggested that the nitrate radical (NO3) plays a role in efficient nighttime oxidation of GEM, and that the role of the hydroxyl radical (OH) as a GEM oxidant has been underestimated. We used the CAABA/MECCA chemical box model and additional kinetic calculations to analyze these measurement results, in order to investigate the nighttime and daytime oxidation of GEM. We assumed a second-order reaction for the NO3 induced nighttime oxidation of GEM. Our analysis demonstrated that nighttime oxidation of GEM has to be included in the model to account for the measured variations in nighttime reactive gaseous mercury (RGM) concentration. A lower limit and best-fit rate constant for GEM nighttime oxidation are provided. To the best of our knowledge, this is the first time that a rate for nighttime oxidation of GEM has been determined based on field measurements. Our analysis further indicates that OH has a much more important role in GEM oxidation than commonly considered. A lower-limit rate constant for the OH–RGM reaction is provided.

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