A 2-year record of atmospheric mercury species at a background Southern Hemisphere station on Amsterdam Island

Angot, Hélène; Barret, Manuel; Magand, Olivier; Ramonet, Michel; Dommergue, Aurélien

doi:10.5194/acp-14-11461-2014

Cited by 66 publications

(95 citation statements)

References 75 publications

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“…php?rubrique3) dedicated to the study of the sulfur cycle at middle and high southern latitudes indicate a mean sodium concentration of 450 ng m −3 between 10 and 14 June 2012 (not shown) instead of 112 ± 62 ng m −3 over the other days of this month. It can be noted that the mean Hg(0) concentration in June 2012 was 0.95 ± 0.04 ng m −3 at TR (Slemr et al, 2015), and 1.02 ± 0.04 ng m −3 on Amsterdam Island (37 • 48 S, 77 • 34 E, Angot et al, 2014). These values are consistent with the increase seen at DDU in air masses arriving from lower latitudes.…”

Section: Resultssupporting

confidence: 79%

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

et al. 2016

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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). This paper also discusses implications for coastal Antarctic ecosystems and for the cycle of atmospheric mercury in high southern latitudes.

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Section: Resultssupporting

confidence: 79%

“…As described by Angot et al (2014), fortnightly to monthly routine maintenance operations were performed. A software program was developed at the LGGE (Laboratoire de Glaciologie et Géophysique de l'Environnement) following quality control practice commonly applied in North American networks (Steffen et al, 2012).…”

Section: Hg(0) Measurementsmentioning

confidence: 99%

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

et al. 2016

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“…In the Southern Hemisphere, Amsterdam Island in the Indian Ocean and Cape Point on the South African coast have similar monthly average concentrations and show no significant seasonal variation (Angot et al, 2014;Slemr et al, 2015). By contrast, the model at those sites has strong seasonality, as previously shown for the standard model version v9-02 .…”

Section: Seasonalitymentioning

confidence: 49%

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

et al. 2017

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Abstract. Mercury (Hg) is emitted to the atmosphere mainly as volatile elemental Hg 0 . Oxidation to water-soluble Hg II plays a major role in Hg deposition to ecosystems. Here, we implement a new mechanism for atmospheric Hg 0 / Hg II redox chemistry in the GEOS-Chem global model and examine the implications for the global atmospheric Hg budget and deposition patterns. Our simulation includes a new coupling of GEOS-Chem to an ocean general circulation model (MITgcm), enabling a global 3-D representation of atmosphereocean Hg 0 / Hg II cycling. We find that atomic bromine (Br) of marine organobromine origin is the main atmospheric Hg 0 oxidant and that second-stage HgBr oxidation is mainly by the NO 2 and HO 2 radicals. The resulting chemical lifetime of tropospheric Hg 0 against oxidation is 2.7 months, shorter than in previous models. Fast Hg II atmospheric reduction must occur in order to match the ∼ 6-month lifetime of Hg against deposition implied by the observed atmospheric variability of total gaseous mercury (TGM ≡ Hg 0 + Hg II (g)). We implement this reduction in GEOS-Chem as photolysis of aqueous-phase Hg II -organic complexes in aerosols and clouds, resulting in a TGM lifetime of 5.2 months against deposition and matching both mean observed TGM and its variability. Model sensitivity analysis shows that the interhemispheric gradient of TGM, previously used to infer a longer Hg lifetime against deposition, is misleading because Southern Hemisphere Hg mainly originates from oceanic emissions rather than transport from the Northern Hemisphere.The model reproduces the observed seasonal TGM variation at northern midlatitudes (maximum in February, minimum in September) driven by chemistry and oceanic evasion, but it does not reproduce the lack of seasonality observed at southern hemispheric marine sites. Aircraft observations in the lowermost stratosphere show a strong TGM-ozone relationship indicative of fast Hg 0 oxidation, but we show that this relationship provides only a weak test of Hg chemistry because it is also influenced by mixing. The model reproduces observed Hg wet deposition fluxes over North America, Europe, and China with little bias (0-30 %). It reproduces qualitatively the observed maximum in US deposition around the Gulf of Mexico, reflecting a combination of deep convection and availability of NO 2 and HO 2 radicals for second-stage HgBr oxidation. However, the magnitude of this maximum is underestimated. The relatively low observed Hg wet deposition over rural China is attributed to fast Hg II reduction in the presence of high organic aerosol concentrations. We find that 80 % of Hg II deposition is to the global oceans, reflecting the marine origin of Br and low concentrations of organic aerosols for Hg II reduction. Most of that deposition takes place to the tropical oceans due to the availability of HO 2 and NO 2 for second-stage HgBr oxidation.

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“…Here, we use the 2009-2012 AMNet observations, as these data are publicly available. AMNet had 23 sites over the continental US and eastern Canada (Nova Scotia) operational during this period (Table S2 in Ground-based measurements of Hg wet deposition and Hg(II) surface concentration have been made as part of the Global Mercury Observations System (GMOS) network (Angot et al, 2014;Wängberg et al, 2016;Sprovieri et al, 2016Sprovieri et al, , 2017Travnikov et al, 2017) and at sites in Europe (Weigelt et al, 2013), Canada, and East Asia (Sheu et al, 2010;Sheu and Lin, 2013;Fu et al, 2015Fu et al, , 2016b. We use the 2013-2014 measurements wherever available but use all sites with 1 year or more of observations.…”

Section: Introductionmentioning

confidence: 99%

Subtropical subsidence and surface deposition of oxidized mercury produced in the free troposphere

Shah

Jaeglé

2017

Atmos. Chem. Phys.

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Abstract. Oxidized mercury (Hg(II)) is chemically produced in the atmosphere by oxidation of elemental mercury and is directly emitted by anthropogenic activities. We use the GEOS-Chem global chemical transport model with gaseous oxidation driven by Br atoms to quantify how surface deposition of Hg(II) is influenced by Hg(II) production at different atmospheric heights. We tag Hg(II) chemically produced in the lower (surface-750 hPa), middle (750-400 hPa), and upper troposphere (400 hPa-tropopause), in the stratosphere, as well as directly emitted Hg(II). We evaluate our 2-year simulation (2013)(2014) against observations of Hg(II) wet deposition as well as surface and free-tropospheric observations of Hg(II), finding reasonable agreement. We find that Hg(II) produced in the upper and middle troposphere constitutes 91 % of the tropospheric mass of Hg(II) and 91 % of the annual Hg(II) wet deposition flux. This large global influence from the upper and middle troposphere is the result of strong chemical production coupled with a long lifetime of Hg(II) in these regions. Annually, 77-84 % of surface-level Hg(II) over the western US, South America, South Africa, and Australia is produced in the upper and middle troposphere, whereas 26-66 % of surface Hg(II) over the eastern US, Europe, and East Asia, and South Asia is directly emitted. The influence of directly emitted Hg(II) near emission sources is likely higher but cannot be quantified by our coarse-resolution global model (2 • latitude × 2.5 • longitude). Over the oceans, 72 % of surface Hg(II) is produced in the lower troposphere because of higher Br concentrations in the marine boundary layer. The global contribution of the upper and middle troposphere to the Hg(II) dry deposition flux is 52 %. It is lower compared to the contribution to wet deposition because dry deposition of Hg(II) produced aloft requires its entrainment into the boundary layer, while rain can scavenge Hg(II) from higher altitudes more readily. We find that 55 % of the spatial variation of Hg wet deposition flux observed at the Mercury Deposition Network sites is explained by the combined variation of precipitation and Hg(II) produced in the upper and middle troposphere. Our simulation points to a large role of the dry subtropical subsidence regions. Hg(II) present in these regions accounts for 74 % of Hg(II) at 500 hPa over the continental US and more than 60 % of the surface Hg(II) over high-altitude areas of the western US. Globally, it accounts for 78 % of the tropospheric Hg(II) mass and 61 % of the total Hg(II) deposition. During the Nitrogen, Oxidants, Mercury, and Aerosol Distributions, Sources, and Sinks (NOMADSS) aircraft campaign, the contribution of Hg(II) from the dry subtropical regions was found to be 75 % when measured Hg(II) exceeded 250 pg m −3 . Hg(II) produced in the upper and middle troposphere subsides in the anticyclones, where the dry conditions inhibit the loss of Hg(II). Our results highlight the importance the subtropical anticyclones as the primary conduits for t...

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A 2-year record of atmospheric mercury species at a background Southern Hemisphere station on Amsterdam Island

Cited by 66 publications

References 75 publications

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

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

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

Subtropical subsidence and surface deposition of oxidized mercury produced in the free troposphere

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