Global Mercury Modelling: Update of Modelling Results in the Global Mercury Assessment 2013.

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AMAP , UNEP , GMA , Mercury
"The Global Mercury Assessment 2013 (GMA 2013) (AMAP/UNEP, 2013) was prepared in accordance with the request of the UNEP’s Governing Council (Decision 25/5 III, paragraph 36) to support negotiations on the development of the Minamata Convention on Mercury, a global treaty to reduce mercury pollution adopted by governments in October 2013. GMA 2013 covered a variety of aspects of the fate and transport of mercury in the environment including emissions to air and releases to the aquatic environment, dispersion and chemical transformations in the atmosphere and aquatic environment, and exchange fluxes between different environmental media. The assessment paid particular attention to the development of an up-to-date global inventory of anthropogenic mercury emissions. Evaluation of mercury pollution on a global scale was based on the analysis of available observational data and modelling results. The current report aims to update the information presented in section 3.6 of the Technical Background Report for the Global Mercury Assessment 2013 (AMAP/UNEP, 2013) with new model simulation results and focusing on an evaluation of mercury intercontinental transport and source attribution of mercury deposition. The character of mercury dispersion in the atmosphere and transport from one region to another is largely affected by the physicochemical properties of the atmospheric mercury species. Poorly soluble and relatively stable gaseous elemental mercury (GEM) can drift in the air for months providing transport of mercury mass between different regions of the planet. In contrast, oxidized mercury species – gaseous oxidized mercury (GOM) and particle bound mercury (PBM) – are easily removed from the air by precipitation scavenging or surface uptake (Selin, 2009; Travnikov, 2011; AMAP/UNEP, 2013). Therefore, levels of mercury deposition and its source apportionment in each region are determined by the magnitude and speciation of domestic emissions, emissions in other regions and by the oxidative capacity of the atmosphere that transforms globally dispersed GEM to deposited GOM and PBM. As has been shown in previous studies (Seigneur et al., 2004; Selin et al., 2008; Travnikov and Ilyin, 2009; Corbitt et al., 2011; Lei et al., 2013; Chen et al., 2014), atmospheric transport from distant sources can make a significant contribution to mercury deposition, particularly in regions with low domestic emissions. On the other hand, the proportion of anthropogenic emissions that deposit locally or regionally depends on emissions speciation, which differs significantly for different emission sectors. Besides, the impact of long-range transport on mercury deposition can vary seasonally due to change in air concentrations of mercury oxidizing agents that lead to change in GEM oxidation intensity and subsequent deposition. The current study is based on multi-model simulations of mercury atmospheric transport performed as part of the Mercury Modelling Task Force (MMTF), a scientific cooperative initiative under the Global Mercury Observation System (GMOS,, aimed at improving current understanding of the key mercury atmospheric processes and evaluating present and future levels of mercury pollution. Simulation results of the multi-model ensemble (see Annex A) are used to quantify global patterns of mercury air concentration and deposition (Chapter 2), source apportionment of mercury deposition to major geographical regions and aquatic areas of the global ocean as well as seasonal variation in source-receptor relationships (Chapter 3), and deposition from different emission sectors (Chapter 4). Simulation results for each individual model of the ensemble are presented in Annex B."