Global atmospheric model for mercury including oxidation by bromine atoms

Holmes, Christopher D.; Jacob, Daniel; Corbitt, Elizabeth S.; Mao, J.; Yang, Xin; Talbot, R. W.; Šlemr, F.

doi:10.5194/acp-10-12037-2010

Cited by 449 publications

(734 citation statements)

References 131 publications

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“…Correlations of TGM with SF 6 suggest a seasonally dependent TGM conversion rate of about 0.43 ng m -3 yr -1 resulting in a stratospheric TGM lifetime of about 2 yr. This lifetime is longer than several weeks claimed recently by Lyman and Jaffe (2012) closer to 1 yr estimated by Holmes et al (2010) using GEOS model with bromine oxidation chemistry.…”

Section: Resultssupporting

confidence: 83%

CARIBIC observations of gaseous mercury in the upper troposphere and lower stratosphere

Šlemr¹,

Ebinghaus

Weigelt

et al. 2013

E3S Web of Conferences

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Abstract.A unique set of gaseous mercury measurements in the upper troposphere and lower stratosphere (UT/LS) has been obtained during the monthly CARIBIC (www.caribic-atmospheric.com) flights since May 2005. The passenger Airbus 340-600 of Lufthansa covered routes to the Far East, North America, India, and the southern hemisphere. The accompanying measurements of CO, O 3 , NOy, H 2 O, aerosols, halocarbons, hydrocarbons, greenhouse gases, and several other parameters as well as backward trajectories enable a detailed analysis of these measurements. Speciation tests have shown that the CARIBIC measurements represent a good approximation of total gaseous mercury (TGM) concentrations. Above the tropopause TGM always decrease with increasing potential vorticity (PV) and O 3 which implies its conversion to particle bound mercury. The observation of the lowest TGM concentrations at the highest particle concentrations in the stratosphere provides further evidence for such conversion. We will show how a seasonally dependent conversion rate could be derived using concomitantly measured SF 6 mixing ratios as a timer. Tropospheric mercury data suggest the existence of a decreasing trend in the northern hemisphere whose size is comparable with the trend derived from long-term measurements by ship cruises, at Cape Point (South Africa) and Mace Head (Ireland).

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Section: Resultssupporting

confidence: 83%

CARIBIC observations of gaseous mercury in the upper troposphere and lower stratosphere

Šlemr¹,

Ebinghaus

Weigelt

et al. 2013

E3S Web of Conferences

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“…This parameterization is based on observed relationships between the gas / particle Hg II concentration ratio and PM 2.5 , and it does not resolve effects from particle composition or surface area. Holmes et al (2010) presented the last detailed global atmospheric budget analysis of Hg in GEOS-Chem, and we use it as a point of comparison for this study. Their model version included Hg 0 oxidation by Br atoms, with Br concentrations specified in the troposphere and stratosphere from the p-TOMCAT and NASA Global Modeling Initiative models, respectively (Yang et al, 2005;Strahan et al, 2007).…”

Section: General Descriptionmentioning

confidence: 99%

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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“…The HgBr + OH rate constant is taken from the assumptions made in Holmes et al (2010). These sensitivity tests are not a direct comparison between the chemical mechanisms, but they are an analysis of how much the atmospheric system changes considering a singular Hg oxidant.…”

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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Global atmospheric model for mercury including oxidation by bromine atoms

Cited by 449 publications

References 131 publications

CARIBIC observations of gaseous mercury in the upper troposphere and lower stratosphere

CARIBIC observations of gaseous mercury in the upper troposphere and lower stratosphere

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

Sensitivity model study of regional mercury dispersion in the atmosphere

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