Multi-model study of mercury dispersion in the atmosphere: Vertical
distribution of mercury species

Šlemr, F.; Ambrose, J. L.; Brenninkmeijer, Carl A. M.; Brooks, Steve; Dastoor, Ashu; DeSimone, Francesco; Ebinghaus, Ralf; Gencarelli, Christian N.; Geyer, Beate; Gratz, Lynne E.; Hedgecock, Ian M.; Jaffe, Daniel A.; Kelley, Paul; Lin, Che‐Jen; Matthias, Volker; Ryjkov, Andrei; Selin, Noelle E.; Song, Shaojie; Travnikov, Oleg; Weigelt, Alexandra; Luke, Winston T.; Ren, X.; Zahn, A.; Yang, Xin; Zhu, Yun; Pirrone, Nicola

doi:10.5194/acp-2016-1074

Cited by 3 publications

(2 citation statements)

References 59 publications

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“…This vertical structure is driven by chemistry (Selin et al, 2007;Holmes et al, 2010), and these general vertical trends in the two species are consistent with limited available observations (Murphy et al, 2006;Talbot et al, 2007;Lyman and Jaffe, 2012). The exact partitioning of total Hg in the stratosphere between Hg 0 and Hg II is uncertain, and GEOS-Chem predicts a higher Hg II fraction relative to other models (Bieser et al, 2016). Photodissociation of gas-phase Hg II halides may be possible at ultraviolet wavelengths (Maya, 1977), but whether this is important in the mid-to-upper stratosphere requires further investigation.…”

Section: Atmosphere-ocean Couplingsupporting

confidence: 76%

Response to anonymous referee #3

Horowitz¹

2017

Preprint

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Section: Atmosphere-ocean Couplingsupporting

confidence: 76%

Response to anonymous referee #3

Horowitz¹

2017

Preprint

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“…Some of these tests have been studied for other regions (e.g. Travnikov et al, 2016 andBieser et al, 2016) while many other studies have investigated Hg oxidation by ozone or Br (Hynes et al, 2009;Subir et al, 2011Subir et al, , 2012WeissPenzias et al, 2015).…”

Section: Simulations Performedmentioning

confidence: 99%

Sensitivity model study of regional mercury dispersion in the atmosphere

et al. 2017

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Abstract. Atmospheric deposition is the most important pathway by which Hg reaches marine ecosystems, where it can be methylated and enter the base of food chain. The deposition, transport and chemical interactions of atmospheric Hg have been simulated over Europe for the year 2013 in the framework of the Global Mercury Observation System (GMOS) project, performing 14 different model sensitivity tests using two high-resolution three-dimensional chemical transport models (CTMs), varying the anthropogenic emission datasets, atmospheric Br input fields, Hg oxidation schemes and modelling domain boundary condition input. Sensitivity simulation results were compared with observations from 28 monitoring sites in Europe to assess model performance and particularly to analyse the influence of anthropogenic emission speciation and the Hg 0 (g) atmospheric oxidation mechanism. The contribution of anthropogenic Hg emissions, their speciation and vertical distribution are crucial to the simulated concentration and deposition fields, as is also the choice of Hg 0 (g) oxidation pathway. The areas most sensitive to changes in Hg emission speciation and the emission vertical distribution are those near major sources, but also the Aegean and the Black seas, the English Channel, the Skagerrak Strait and the northern German coast. Considerable influence was found also evident over the Mediterranean, the North Sea and Baltic Sea and some influence is seen over continental Europe, while this difference is least over the north-western part of the modelling domain, which includes the Norwegian Sea and Iceland. The Br oxidation pathway produces more Hg II (g) in the lower model levels, but overall wet deposition is lower in comparison to the simulations which employ an O 3 / OH oxidation mechanism. The necessity to perform continuous measurements of speciated Hg and to investigate the local impacts of Hg emissions and deposition, as well as interactions dependent on land use and vegetation, forests, peat bogs, etc., is highlighted in this study.

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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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Multi-model study of mercury dispersion in the atmosphere: Vertical distribution of mercury species

Cited by 3 publications

References 59 publications

Response to anonymous referee #3

Response to anonymous referee #3

Sensitivity model study of regional mercury dispersion in the atmosphere

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

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