Abstract
In the atmosphere mercury exists in three forms: Gaseous Elemental Mercury (GEM), Gaseous Oxidized Mercury (GOM), and Particle Bound Mercury (PBM). GOM and PBM make up only 1 % of the total. But deposition, which is the only sink for atmospheric mercury, is dominated by these two species. Therefore, oxidation processes are key to understand the behaviour of mercury in the atmosphere. However, in the scientific community a consensus on the importance of oxidizing reactants, namely ozone, hydroxy radicals, and halogens, has not been reached.
This model study about the influence of chemical reactants on the regional transport of mercury is part of the European Union FP7 Research Project GMOS (Global Mercury Observation System). GMOS focuses on the improvement and validation of mercury models to assist establishing a global monitoring network and to support political decisions.
In the course of this study the Community Multiscale Air Quality (CMAQ) model was used to simulate the transport and deposition of mercury. CMAQ was run on a regional domain over Europe using different chemical mechanisms for the oxidation of mercury. The model results were compared to newly available long term observations of speciated mercury. Based on this unique dataset, the relevance of different chemical reactions for the oxidation and reduction of mercury were investigated. The main finding was that the emissions of GOM as well as the production of GOM by oxidation processes is vastly overestimated. Moreover, there are indicators that the fraction of PBM, produced by reaction of GEM with ozone and OH is overestimated.
DOI Link to Publication