European and Mediterranean mercury modelling: local and long-range contributions to the deposition flux

Mercury (Hg) is a global pollutant that is known to have adverse effects on human health, and most human exposure to toxic methylmercury is through fish consumption. Soluble Hg compounds in the marine environment can be methylated in the water column and enter the base of the food chain. Atmospheric deposition is the most important pathway by which Hg enters marine ecosystems. The atmospheric chemistry of Hg has been simulated over Europe and the Mediterranean for the year 2009, using the WRF/Chem model and employing two different gas phase Hg oxidation mechanisms. The contributions to the marine deposition flux from dry deposition, synoptic scale wet deposition and convective wet deposition have been determined. The Hg deposition fluxes resulting from transcontinental transport and local/regional emission sources has been determined using both Br/BrO and O3/OH atmospheric oxidation mechanisms. The two mechanisms give significantly different annual deposition fluxes (129 Mg and 266 Mg respectively) over the modelling domain. Dry deposition is more significant using the O3/OH mechanism, while proportionally convective wet deposition is enhanced using the Br/BrO mechanism. The simulations using the Br/BrO oxidation compared best with observed Hg fluxes in precipitation. Local/regional Hg emissions have the most impact within the model domain during the summer. A comparison of simulations using the 2005 and 2010 AMAP/UNEP Hg emission inventories show that although there is a decrease of 33% in anthropogenic emissions between the two reference years, the total simulated deposition in the regions diminishes by only 12%. Simulations using the 2010 inventory reproduce observations somewhat better than those using the 2005 inventory for 2009

Model study of global mercury deposition from biomass burning

Mercury emissions from biomass burning are not well characterized and can differ significantly from year to year. This study utilizes three recent biomass burning inventories (FINNv1.0, GFEDv3.1, and GFASv1.0) and the global Hg chemistry model, ECHMERIT, to investigate the annual variation of Hg emissions, and the geographical distribution and magnitude of the resulting Hg deposition fluxes. The roles of the Hg/CO enhancement ratio, the emission plume injection height, the Hg(g)0 oxidation mechanism and lifetime, the inventory chosen, and the uncertainties with each were considered. The greatest uncertainties in the total Hg deposition were found to be associated with the Hg/CO enhancement ratio and the emission inventory employed. Deposition flux distributions proved to be more sensitive to the emission inventory and the oxidation mechanism chosen, than all the other model parametrizations. Over 75% of Hg emitted from biomass burning is deposited to the world’s oceans, with the highest fluxes predicted in the North Atlantic and the highest total deposition in the North Pacific. The net effect of biomass burning is to liberate Hg from lower latitudes and disperse it toward higher latitudes where it is eventually deposited

The GOS4M Knowledge Hub: A web-based effectiveness evaluation platform in support of the Minamata Convention on Mercury

Abstract The Minamata Convention on Mercury was established to reduce the pressure on the environment caused by mercury by significantly reducing its emissions from anthropogenic activities. However, knowledge gaps still exist concerning emission inventories, emission factors and their integration in modelling frameworks. In addition, tools to facilitate communication between decision-makers and research groups providing measurement and modelling data are still scarce. This work presents the GOS4M Knowledge Hub, a public web application that provides an interactive and user friendly experience to access state-of-the-art modelling tools and data available in the literature. The Knowledge Hub currently integrates a Chemical Transport Model emulator, HERMES, coupled with a biogeochemical model, although it has been designed to house and deploy any number of different modelling components. Using the integrated dashboard, non-experts can perturb mercury releases from different anthropogenic emission sectors, simulating, for example, the application of Best Available Technologies, and then visualise in real-time the short- and long-term effects of the consequent reductions within a source-receptor framework. The dashboard also furnishes an estimate of the statistical significance of the changes in the model results. The analysis of a set of anthropogenic Hg emission reduction scenarios shows how an internationally coordinated effort would be necessary to achieve significant policy goals. It is important to note that the GOS4M Knowledge Hub yields the analysis presented here in a matter of seconds, compared to the days or weeks required by traditional modelling tools

Scaling Properties of Atmospheric Wind Speed in Mesoscale Range

The scaling properties of turbulent flows are well established in the inertial sub-range. However, those of the synoptic-scale motions are less known, also because of the difficult analysis of data presenting nonstationary and periodic features. Extensive analysis of experimental wind speed data, collected at the Mauna Loa Observatory of Hawaii, is performed using different methods. Empirical Mode Decomposition, interoccurrence times statistics, and arbitrary-order Hilbert spectral analysis allow to eliminate effects of large-scale modulations, and provide scaling properties of the field fluctuations (Hurst exponent, interoccurrence distribution, and intermittency correction). The obtained results suggest that the mesoscale wind dynamics owns features which are typical of the inertial sub-range turbulence, thus extending the validity of the turbulent cascade phenomenology to scales larger than observed before

A Chemical Transport Model Emulator for the Interactive Evaluation of Mercury Emission Reduction Scenarios

Implementation of the Minamata Convention on Mercury requires all parties to "control, and where feasible, reduce" mercury (Hg) emissions from a convention-specified set of sources. However, the convention does not specify the extent of the measures to be adopted, which may only be analysed by decision-makers using modelled scenarios. Currently, the numerical models available to study the Hg atmospheric cycle require significant expertise and high-end hardware, with results which are generally available on a time frame of days to weeks. In this work we present HERMES, a statistical emulator built on the output of a global Chemical Transport Model (CTM) for Hg (ECHMERIT), to simulate changes in anthropogenic Hg (Hganthr) deposition fluxes in a source-receptor framework, due to perturbations to Hganthr emissions and the associated statistical significance of the changes. The HERMES emulator enables stakeholders to evaluate the implementation of different Hganthr emission scenarios in an interactive and real-time manner, simulating the application of the different Best Available Technologies. HERMES provides the scientific soundness of a full CTM numerical framework in an interactive and user-friendly spreadsheet, without the necessity for specific training or formation and is a first step towards a more comprehensive, and integrated, decision support system to aid decision-makers in the implementation of the Minamata Convention

Current and future levels of mercury atmospheric pollution on global scale

An assessment of current and future emissions, air concentrations and atmospheric deposition of mercury world-wide are 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 artisanal and small- scale gold mining, as well as combustion of fossil fuels (mainly coal) for energy and heat production in power plants and in industrial and residential boilers are 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 tonnes. The emissions in Asian countries, particularly in China and India dominate the total emissions of Hg. The current estimate of mercury emissions from natural processes (primary mercury emissions and re-emissions), including mercury depletion events, were estimated to be 5207 tonnes per year which represent 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 3 different scenarios with current anthriopogenic 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 Hg pollution levels considering future emission scenarios. Projections of future changes in Hg deposition on a global scale simulated by these models for three anthropogenic emissions scenarios of 2035 indicate a decrease of 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, first the scientific justification for the Minamata Convention, and then 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 Hg on global and regional scale, and source – receptor techniques for Hg emission apportionment on a global scale.</p

Multi-model study of mercury dispersion in the atmosphere : Atmospheric processes and model evaluation

Current understanding of mercury (Hg) behavior in the atmosphere contains significant gaps. Some key characteristics of Hg processes, including anthropogenic and geogenic emissions, atmospheric chemistry, and air-surface exchange, are still poorly known. This study provides a complex analysis of processes governing Hg fate in the atmosphere involving both measured data from ground-based sites and simulation results from chemical transport models. A variety of long-term measurements of gaseous elemental Hg (GEM) and reactive Hg (RM) concentration as well as Hg wet deposition flux have been compiled from different global and regional monitoring networks. Four contemporary global-scale transport models for Hg were used, both in their state-of-the-art configurations and for a number of numerical experiments to evaluate particular processes. Results of the model simulations were evaluated against measurements. As follows from the analysis, the interhemispheric GEM gradient is largely formed by the prevailing spatial distribution of anthropogenic emissions in the Northern Hemisphere. The contributions of natural and secondary emissions enhance the south-to-north gradient, but their effect is less significant. Atmospheric chemistry has a limited effect on the spatial distribution and temporal variation of GEM concentration in surface air. In contrast, RM air concentration and wet deposition are largely defined by oxidation chemistry. The Br oxidation mechanism can reproduce successfully the observed seasonal variation of the RM=GEM ratio in the near-surface layer, but it predicts a wet deposition maximum in spring instead of in summer as observed at monitoring sites in North America and Europe. Model runs with OH chemistry correctly simulate both the periods of maximum and minimum values and the amplitude of observed seasonal variation but shift the maximum RM=GEM ratios from spring to summer. O3 chemistry does not predict significant seasonal variation of Hg oxidation. Hence, the performance of the Hg oxidation mechanisms under study differs in the extent to which they can reproduce the various observed parameters. This variation implies possibility of more complex chemistry and multiple Hg oxidation pathways occurring concurrently in various parts of the atmosphere