. Mercury (Hg) is emitted to the atmosphere mainly as volatile elemental Hg0. Oxidation to water-soluble HgII plays a major role in Hg deposition to ecosystems. Here, we implement a new mechanism for atmospheric Hg0 ∕ HgII 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 atmosphere–ocean Hg0 ∕ HgII cycling. We find that atomic bromine (Br) of marine organobromine origin is the main atmospheric Hg0 oxidant and that second-stage HgBr oxidation is mainly by the NO2 and HO2 radicals. The resulting chemical lifetime of tropospheric Hg0 against oxidation is 2.7 months, shorter than in previous models. Fast HgII 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  ≡  Hg0 + HgII(g)). We implement this reduction in GEOS-Chem as photolysis of aqueous-phase HgII–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 Hg0 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 NO2 and HO2 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 HgII reduction in the presence of high organic aerosol concentrations. We find that 80 % of HgII deposition is to the global oceans, reflecting the marine origin of Br and low concentrations of organic aerosols for HgII reduction. Most of that deposition takes place to the tropical oceans due to the availability of HO2 and NO2 for second-stage HgBr oxidation.

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

https://biblio.ugent.be/publication/8632517/file/8632518.pdf

Mercury speciation, transformation, and transportation in soils, atmospheric flux, and implications for risk management: A critical review

Precipitation of energetic particles into the atmosphere greatly disturbs the chemical composition from the upper stratosphere to the lower thermosphere. Most important are changes to the budget of atmospheric nitric oxides (NOx = N, NO, NO2) and to atmospheric reactive hydrogen oxides (HOx = H, OH, HO2), which both contribute to ozone loss in the stratosphere and mesosphere. The impact of energetic particle precipitation on the chemical composition of the atmosphere has been studied since the 1960s, and there are a number of observations as well as model studies concerning especially the auroral impact and large solar particle events. Changes to the NOx budget due to energetic particle precipitation can be quite long-lived during polar winter and can then be transported down into the lower mesosphere and stratosphere, where NOx is one of the main participants in catalytic ozone destruction. Energetic particle precipitation can also affect temperatures and dynamics of the atmosphere from the source region down to the stratosphere and possibly even down to the surface, due to a coupling of chemical composition changes affecting atmospheric heating and cooling rates, the mean circulation, and wave propagation and breaking. Thus, energetic particle precipitation impacts have been implemented in chemistry-climate models reaching from the surface up to the mesosphere or lower thermosphere. However, there are still a number of open questions in the theoretical description of the energetic particle precipitation impact; the most important are uncertainties in the formation rate of different NOx species due to energetic particle precipitation, and the complex coupling between chemical changes, atmospheric heating and cooling rates, and atmospheric dynamics.

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Energetic Particle Precipitation and the Chemistry of the Mesosphere/Lower Thermosphere

This study presents the first measurement of Hg stable isotope fractionation during gas-phase oxidation of Hg0 vapor by halogen atoms (Cl•, Br•) in the laboratory at 750 ± 1 Torr and 298 ± 3 K. Using a relative rate technique, the rate coefficients for Hg0+Cl• and Hg0+Br• reactions are determined to be (1.8 ± 0.5) × 10–11 and (1.6 ± 0.8) × 10–12 cm3 molecule–1 s–1, respectively. Results show that heavier isotopes are preferentially enriched in the remaining Hg0 during Cl• initiated oxidation, whereas being enriched in the product during oxidation by Br•. The fractionation factors for 202Hg/198Hg during the Cl• and Br• initiated oxidations are α202/198 = 0.99941 ± 0.00006 (2σ) and 1.00074 ± 0.00014 (2σ), respectively. A Δ199Hg/Δ201Hg ratio of 1.64 ± 0.30 (2σ) during oxidation of Hg0 by Br atoms suggests that Hg-MIF is introduced by the nuclear volume effect (NVE). In contrast, the Hg0 + Cl• reaction produces a Δ199Hg/Δ201Hg-slope of 1.89 ± 0.18 (2σ), which in addition to a high degree of odd-mass-number is...

Mass-Dependent and -Independent Fractionation of Mercury Isotope during Gas-Phase Oxidation of Elemental Mercury Vapor by Atomic Cl and Br.

. An assessment of current and future emissions, air concentrations, and atmospheric deposition of mercury worldwide is presented on the basis of results obtained during the performance of the EU GMOS (Global Mercury Observation System) project. Emission estimates for mercury were prepared with the main goal of applying them in models to assess current (2013) and future (2035) air concentrations and atmospheric deposition of this contaminant. The combustion of fossil fuels (mainly coal) for energy and heat production in power plants and in industrial and residential boilers, as well as artisanal and small-scale gold mining, is one of the major anthropogenic sources of Hg emissions to the atmosphere at present. These sources account for about 37 and 25 % of the total anthropogenic Hg emissions globally, estimated to be about 2000 t. Emissions in Asian countries, particularly in China and India, dominate the total emissions of Hg. The current estimates of mercury emissions from natural processes (primary mercury emissions and re-emissions), including mercury depletion events, were estimated to be 5207 t year−1, which represents nearly 70 % of the global mercury emission budget. Oceans are the most important sources (36 %), followed by biomass burning (9 %). A comparison of the 2035 anthropogenic emissions estimated for three different scenarios with current anthropogenic emissions indicates a reduction of these emissions in 2035 up to 85 % for the best-case scenario. Two global chemical transport models (GLEMOS and ECHMERIT) have been used for the evaluation of future mercury pollution levels considering future emission scenarios. Projections of future changes in mercury deposition on a global scale simulated by these models for three anthropogenic emissions scenarios of 2035 indicate a decrease in up to 50 % deposition in the Northern Hemisphere and up to 35 % in Southern Hemisphere for the best-case scenario. The EU GMOS project has proved to be a very important research instrument for supporting the scientific justification for the Minamata Convention and monitoring of the implementation of targets of this convention, as well as the EU Mercury Strategy. This project provided the state of the art with regard to the development of the latest emission inventories for mercury, future emission scenarios, dispersion modelling of atmospheric mercury on a global and regional scale, and source–receptor techniques for mercury emission apportionment on a global scale.

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Current and future levels of mercury atmospheric pollution on a global scale

Atmosphere and at Atmospheric Interfaces: A Review and Future Directions Parisa A. Ariya,*,†,‡ Marc Amyot, Ashu Dastoor, Daniel Deeds,‡ Aryeh Feinberg,† Gregor Kos,‡ Alexandre Poulain, Andrei Ryjkov, Kirill Semeniuk, M. Subir, and Kenjiro Toyota †Department of Chemistry and ‡Department of Atmospheric and Oceanic Sciences, McGill University, 801 Sherbrooke Street West, Montreal, Quebec, Canada, H3A 2K6 Department of Biological Sciences, Universite ́ de Montreál, 90 avenue Vincent-d’Indy, Montreal, Quebec, Canada, H3C 3J7 Air Quality Research Division, Environment Canada, 2121 TransCanada Highway, Dorval, Quebec, Canada, H9P 1J3 Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, Canada, K1N 6N5 Department of Chemistry, Ball State University, 2000 West University Avenue, Muncie, Indiana 47306, United States Air Quality Research Division, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, Canada, M3H 5T4

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Mercury physicochemical and biogeochemical transformation in the atmosphere and at atmospheric interfaces: a review and future directions.

B. Funke1, M. Garcia-Comas1, M. Lopez-Puertas1, N. Glatthor2, G. P. Stiller2, T. von Clarmann2, K. Semeniuk3, and J. C. McConnell3 1Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain 2Forschungszentrum Karlsruhe und Universitat Karlsruhe, Institut fur Meteorologie und Klimaforschung, Karlsruhe, Germany 3Department of Earth and Space Science and Engineering, York University, Toronto, Ontario, Canada

Kirill Semeniuk

Papers

Mercury physicochemical and biogeochemical transformation in the atmosphere and at atmospheric interfaces: a review and future directions.

Enhancement of N2O during the October–November 2003 solar proton events