Photoreduction of gaseous oxidized mercury changes global atmospheric mercury speciation, transport and deposition

Saiz‐Lopez, Alfonso; Sitkiewicz, Sebastian P.; Roca‐Sanjuán, Daniel; Oliva‐Enrich, Josep M.; Dávalos, Juan Z.; Notario, Rafael; Jiskra, Martin; Yang, Xu; Wang, Fei; Thackray, Colin P.; Sunderland, Elsie M.; Jacob, Daniel; Travnikov, Oleg; Cuevas, Carlos A.; Acuña, A. Ulises; Rivero, Daniel; Plane, J. M. C.; Kinnison, Douglas E.; Sonke, Jeroen E.

doi:10.1038/s41467-018-07075-3

Cited by 136 publications

(201 citation statements)

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“…The Hg that is emitted from anthropogenic (and natural) sources to air is almost exclusively inorganic as elemental (Hg 0 ) and divalent compounds (Hg II ) in gaseous and particulate forms (Obrist et al, 2018). Redox reactions between Hg 0 and Hg II in the atmosphere are primarily photochemically driven (Ariya et al, 2015;Saiz-Lopez et al, 2018), with the bulk of the atmospheric Hg deposited onto the Earth's surface (oceans, land, and freshwaters) being in the form of inorganic Hg II . The aquatic environment also receives Hg input, primarily as inorganic Hg II , from rivers,…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, the relationship between anthropogenic Hg emissions to the atmosphere and Hg trends in aquatic biota is influenced by many environmental and ecological factors (e.g., temperature, light intensity, pH, redox condition, organic carbon and nutrient concentrations, and food web structure and dynamics) that control the rates of Hg deposition from the atmosphere, MeHg production (methylation) and degradation (demethylation) in the aquatic environment, and the uptake of Hg, especially MeHg, by biota Hsu-Kim et al, 2018). The complexity of these processes, along with the large inventories of legacy anthropogenic and natural Hg stored long-term in terrestrial and aquatic systems, suggests that biotic Hg may be only tenuously connected to atmospheric Hg which has a much shorter life-time (0.5 to 2 years) than the decadal or century-scale life-times of Hg in soils and oceans (Horowitz et al, 2017;Saiz-Lopez et al, 2018). Furthermore, even if atmospheric and biotic Hg do follow similar trends, there could be a significant time lag between their response.…”

Section: Introductionmentioning

confidence: 99%

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How closely do mercury trends in fish and other aquatic wildlife track those in the atmosphere? – Implications for evaluating the effectiveness of the Minamata Convention

Wang

Outridge

Meng

et al. 2019

Science of The Total Environment

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

How closely do mercury trends in fish and other aquatic wildlife track those in the atmosphere? – Implications for evaluating the effectiveness of the Minamata Convention

Wang

Outridge

Meng

et al. 2019

Science of The Total Environment

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“…The Hg 0 flux measured at the CH-Cha site is comparable to Hg 0 fluxes reported for other grassland sites worldwide . A median Hg 0 flux of 0.4 ng m −2 h −1 and a flux range between −18.7 and 41.5 ng m −2 h −1 (site-based average fluxes) was reported for nine studies (Poissant and Casimir, 1998;Schroeder et al, 2005;Ericksen et al, 2006;Obrist et al, 2006;Fu et al, 2008a, b;Fritsche et al 2008a, b;Converse et al, 2010). Several studies reported net Hg 0 emission during summer.…”

Section: Net Ecosystem Exchange Of Hg 0 Over Grasslandmentioning

confidence: 97%

Eddy covariance flux measurements of gaseous elemental mercury over a grassland

et al. 2020

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Direct measurements of the net ecosystem exchange (NEE) of gaseous elemental mercury (Hg 0 ) are important to improve our understanding of global Hg cycling and, ultimately, human and wildlife Hg exposure. The lack of long-term, ecosystem-scale measurements causes large uncertainties in Hg 0 flux estimates. It currently remains unclear whether terrestrial ecosystems are net sinks or sources of atmospheric Hg 0 . Here, we show a detailed validation of direct Hg 0 flux measurements based on the eddy covariance technique (Eddy Mercury) using a Lumex RA-915 AM mercury monitor. The flux detection limit derived from a zero-flux experiment in the laboratory was 0.22 ng m −2 h −1 (maximum) with a 50 % cutoff at 0.074 ng m −2 h −1 . We present eddy covariance NEE measurements of Hg 0 over a low-Hg soil (41-75 ng Hg g −1 in the topsoil, referring to a depth of 0-10 cm), conducted in summer 2018 at a managed grassland at the Swiss FluxNet site in Chamau, Switzerland (CH-Cha). The statistical estimate of the Hg 0 flux detection limit under outdoor conditions at the site was 5.9 ng m −2 h −1 (50 % cutoff). We measured a net summertime emission over a period of 34 d with a median Hg 0 flux of 2.5 ng m −2 h −1 (with a −0.6 to 7.4 ng m −2 h −1 range between the 25th and 75th percentiles). We observed a distinct diel cycle with higher median daytime fluxes (8.4 ng m −2 h −1 ) than nighttime fluxes (1.0 ng m −2 h −1 ). Drought stress during the measurement campaign in summer 2018 induced partial stomata closure of vegetation. Partial stomata closure led to a midday depression in CO 2 uptake, which did not recover during the afternoon. The median CO 2 flux was only 24 % of the median CO 2 flux measured during the same period in the previous year (2017). We suggest that partial stomata closure also dampened Hg 0 uptake by vegetation, resulting in a NEE of Hg 0 that was dominated by soil emission. Finally, we provide suggestions to further improve the precision and handling of the "Eddy Mercury" system in order to assure its suitability for long-term NEE measurements of Hg 0 over natural background surfaces with low soil Hg concentrations (< 100 ng g −1 ). With these improvements, Eddy Mercury has the potential to be integrated into global networks of micrometeorological tower sites (FluxNet) and to provide the longterm observations on terrestrial atmosphere Hg 0 exchange necessary to validate regional and global mercury models.

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“…The spring period selected for the 2016 experiment had two main characteristics: a welldefined night and day cycle without a long sunset, avoiding possible incoming solar radiation by diffraction processes over the horizon. There was also the possibility observing atmospheric mercury depletion events (AMDEs) connected with bromine explosion events (Lu et al, 2001;Moore et al, 2014;Schroeder and Munthe, 1998). Unfortunately, these events were not observed as the northern coast of Svalbard was virtually ice free by the time we started sampling.…”

Section: Sampling Period and Strategymentioning

confidence: 99%

“…Mercury is a heavy metal with a known toxicity present in the environment in several different chem-ical forms. It is reactive in the environment and undergoes photochemical reactions that change its speciation and chemical behaviour (Dommergue et al, 2010;Durnford and Dastoor, 2011;Saiz-Lopez et al, 2018;Steffen et al, 2002). Mercury in its oxidized form can be deposited onto the snowpack, increasing Hg concentrations in the upper snow strata (Obrist et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Diurnal cycle of iodine, bromine, and mercury concentrations in Svalbard surface snow

Spolaor¹,

Barbaro²,

Cappelletti

et al. 2019

Atmos. Chem. Phys.

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Abstract. Sunlit snow is highly photochemically active and plays a key role in the exchange of gas phase species between the cryosphere and the atmosphere. Here, we investigate the behaviour of two selected species in surface snow: mercury (Hg) and iodine (I). Hg can deposit year-round and accumulate in the snowpack. However, photo-induced re-emission of gas phase Hg from the surface has been widely reported. Iodine is active in atmospheric new particle formation, especially in the marine boundary layer, and in the destruction of atmospheric ozone. It can also undergo photochemical re-emission. Although previous studies indicate possible post-depositional processes, little is known about the diurnal behaviour of these two species and their interaction in surface snow. The mechanisms are still poorly constrained, and no field experiments have been performed in different seasons to investigate the magnitude of re-emission processes Three sampling campaigns conducted at an hourly resolution for 3 d each were carried out near Ny-Ålesund (Svalbard) to study the behaviour of mercury and iodine in surface snow under different sunlight and environmental conditions (24 h darkness, 24 h sunlight and day–night cycles). Our results indicate a different behaviour of mercury and iodine in surface snow during the different campaigns. The day–night experiments demonstrate the existence of a diurnal cycle in surface snow for Hg and iodine, indicating that these species are indeed influenced by the daily solar radiation cycle. Differently, bromine did not show any diurnal cycle. The diurnal cycle also disappeared for Hg and iodine during the 24 h sunlight period and during 24 h darkness experiments supporting the idea of the occurrence (absence) of a continuous recycling or exchange at the snow–air interface. These results demonstrate that this surface snow recycling is seasonally dependent, through sunlight. They also highlight the non-negligible role that snowpack emissions have on ambient air concentrations and potentially on iodine-induced atmospheric nucleation processes.

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Photoreduction of gaseous oxidized mercury changes global atmospheric mercury speciation, transport and deposition

Cited by 136 publications

References 71 publications

How closely do mercury trends in fish and other aquatic wildlife track those in the atmosphere? – Implications for evaluating the effectiveness of the Minamata Convention

How closely do mercury trends in fish and other aquatic wildlife track those in the atmosphere? – Implications for evaluating the effectiveness of the Minamata Convention

Eddy covariance flux measurements of gaseous elemental mercury over a grassland

Diurnal cycle of iodine, bromine, and mercury concentrations in Svalbard surface snow

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