An analysis of simulated wet deposition of mercury from the North American Mercury Model Intercomparison Study

Bullock, O. Russell; Atkinson, Dwight; Braverman, Thomas; Civerolo, Kevin; Dastoor, Ashu; Davignon, Didier; Ku, Jia‐Yeong; Lohman, Kristen; Myers, Thomas C.; Park, Rokjin J.; Seigneur, Christian; Selin, Noelle E.; Sistla, Gopal; Vijayaraghavan, Krish

doi:10.1029/2008jd011224

Cited by 60 publications

(51 citation statements)

References 16 publications

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“…Both MDN and EMEP have been used extensively to test atmospheric mercury models (e.g. Bullock et al, 2009;Gusev et al, 2009) and to evaluate the impact of mercury emission reductions (e.g. Butler et al, 2008;Wangberg et al, 2007;Pacyna et al, 2009;Prestbo and Gay, 2009).…”

Section: Testing Oxidation Chemistry Through Antarctic Subsidence Eventsmentioning

confidence: 99%

“…The above model studies derived their tropospheric bromine concentrations from satellite observations of BrO columns (Chance, 1998;Burrows et al, 1999), which feature polar maxima of BrO. Recent aircraft observations in the Arctic, however, show that the troposphere contributes less to these polar maxima than previously expected (Salawitch et al, 2010), so earlier models likely overestimated tropospheric Hg 0 oxidation at high latitudes.…”

Section: Introductionmentioning

confidence: 99%

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Global atmospheric model for mercury including oxidation by bromine atoms

et al. 2010

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Abstract. Global models of atmospheric mercury generally assume that gas-phase OH and ozone are the main oxidants converting Hg 0 to Hg II and thus driving mercury deposition to ecosystems. However, thermodynamic considerations argue against the importance of these reactions. We demonstrate here the viability of atomic bromine (Br) as an alternative Hg 0 oxidant. We conduct a global 3-D simulation with the GEOS-Chem model assuming gas-phase Br to be the sole Hg 0 oxidant (Hg + Br model) and compare to the previous version of the model with OH and ozone as the sole oxidants (Hg + OH/O 3 model). We specify global 3-D Br concentration fields based on our best understanding of tropospheric and stratospheric Br chemistry. In both the Hg + Br and Hg + OH/O 3 models, we add an aqueous photochemical reduction of Hg II in cloud to impose a tropospheric lifetime for mercury of 6.5 months against deposition, as needed to reconcile observed total gaseous mercury (TGM) concentrations with current estimates of anthropogenic emissions. This added reduction would not be necessary in the Hg + Br model if we adjusted the Br oxidation kinetics downward within their range of uncertainty. We find that the Hg + Br and Hg + OH/O 3 models are equally capable of reproducing the spatial distribution of TGM and its seasonal cycle at northern mid-latitudes. The Hg + Br model shows a steeper decline of TGM concentrations from the tropics to southern mid-latitudes. Only the Hg + Br model can reproduce the springtime depletion and summer rebound of TGM observed at polar sites; the snowpack component of GEOS-Chem suggests that 40% of Hg II deposited to snow in the Arctic is transferred to the ocean and land reservoirs, amounting to aCorrespondence to: C. D. Holmes (cdholmes@post.harvard.edu) net deposition flux to the Arctic of 60 Mg a −1 . Summertime events of depleted Hg 0 at Antarctic sites due to subsidence are much better simulated by the Hg + Br model. Model comparisons to observed wet deposition fluxes of mercury in the US and Europe show general consistency. However the Hg + Br model does not capture the summer maximum over the southeast US because of low subtropical Br concentrations while the Hg + OH/O 3 model does. Vertical profiles measured from aircraft show a decline of Hg 0 above the tropopause that can be captured by both the Hg + Br and Hg + OH/O 3 models, except in Arctic spring where the observed decline is much steeper than simulated by either model; we speculate that oxidation by Cl species might be responsible. The Hg + Br and Hg + OH/O 3 models yield similar global budgets for the cycling of mercury between the atmosphere and surface reservoirs, but the Hg + Br model results in a much larger fraction of mercury deposited to the Southern Hemisphere oceans.

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Section: Testing Oxidation Chemistry Through Antarctic Subsidence Eventsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Global atmospheric model for mercury including oxidation by bromine atoms

et al. 2010

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“…In a recent review Ariya et al (2015) give a exhaustive summary of modelling progress and of the uncertainties still present concerning the atmospheric Hg cycle. To date only a limited number of model-to-model intercomparisons have been carried out (for the US: Bullock et al, 2008Bullock et al, , 2009Zhang et al, 2012;for Europe: Ryaboshapko et al, 2007; for global models: Travnikov et al, 2010Travnikov et al, , 2016AMAP/UNEP, 2013), where it was found that are often significant differences in Hg concentrations and deposition estimated by different models. Previous European studies (Ryaboshapko et al, 2007) performed a model intercomparison for the year 1999, using eight different models and data from 11 measurement stations with the aim to characterise the ability of CTMs to predict atmospheric Hg concentration and deposition fields.…”

Section: Introductionmentioning

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 significant problem with this approach, however, is that the regional and global models often use different assumptions about Hg emissions, chemistry, deposition, and meteorology. Use of different global models to define boundary conditions leads to large variations in regional patterns of atmospheric Hg concentrations, as well as wet and dry deposition (Bullock et al, 2008(Bullock et al, , 2009Pongprueksa et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Nested-grid simulation of mercury over North America

et al. 2012

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Abstract. We have developed a new nested-grid mercury (Hg) simulation over North America with a 1/2 • latitude by 2/3 • longitude horizontal resolution employing the GEOSChem global chemical transport model. Emissions, chemistry, deposition, and meteorology are self-consistent between the global and nested domains. Compared to the global model (4 • latitude by 5 • longitude), the nested model shows improved skill at capturing the high spatial and temporal variability of Hg wet deposition over North America observed by the Mercury Deposition Network (MDN) in [2008][2009]. The nested simulation resolves features such as higher deposition due to orographic precipitation, land/ocean contrast and and predicts more efficient convective rain scavenging of Hg over the southeast United States. However, the nested model overestimates Hg wet deposition over the Ohio River Valley region (ORV) by 27 %. We modify anthropogenic emission speciation profiles in the US EPA National Emission Inventory (NEI) to account for the rapid inplume reduction of reactive to elemental Hg (IPR simulation). This leads to a decrease in the model bias to −2.3 % over the ORV region. Over the contiguous US, the correlation coefficient (r) between MDN observations and our IPR simulation increases from 0.60 to 0.78. The IPR nested simulation generally reproduces the seasonal cycle in surface concentrations of speciated Hg from the Atmospheric Mercury Network (AMNet) and Canadian Atmospheric Mercury Network (CAMNet). In the IPR simulation, annual mean gaseous and particulate-bound Hg(II) are within 140 % and 11 % of observations, respectively. In contrast, the simulation with unmodified anthropogenic Hg speciation profiles overestimates these observations by factors of 4 and 2 for gaseous and particulate-bound Hg(II), respectively. The nested model shows improved skill at capturing the horizontal variability of Hg observed over California during the ARCTAS aircraft campaign. The nested model suggests that North American anthropogenic emissions account for 10-22 % of Hg wet deposition flux over the US, depending on the anthropogenic emissions speciation profile assumed. The modeled percent contribution can be as high as 60 % near large point sources in ORV. Our results indicate that the North American anthropogenic contribution to dry deposition is 13-20 %.

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An analysis of simulated wet deposition of mercury from the North American Mercury Model Intercomparison Study

Cited by 60 publications

References 16 publications

Global atmospheric model for mercury including oxidation by bromine atoms

Global atmospheric model for mercury including oxidation by bromine atoms

Sensitivity model study of regional mercury dispersion in the atmosphere

Nested-grid simulation of mercury over North America

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