Mercury oxidations and deposition: an European model analysis

A modified version of the WRF/Chem model has been developed within the GMOS project in order to include the concentration fields and deposition fluxes of mercury. Thus anthropogenic and natural emissions, gaseous and aqueous phase oxidation, transport and deposition of atmospheric mercury were implemented in this model version [1]. Using the WRF/Chem with Hg model simulations of the atmospheric mercury cycle over Europe and the Mediterranean Basin for the year 2009 have been performed using the most recent AMAP/UNEP emissions (for the year 2010). Also chemical initial and boundary conditions from ECHMERIT global on-line chemical transport model [2] were used. Due to the continuing debate over the precise atmospheric Hg oxidation mechanism [3], simulations using a Br/BrO based Hg oxidation mechanism rather than O3/OH were performed. Utilising the Br oxidation mechanism a third of Hg deposition occurs over the seas, while in the O3/OH simulation it is only one quarter. The results reinforce the view that the gas phase conversion of Hg0(g) to HgII (g) by Br is more consistent with observational data and in particular with measured Hg fluxes in precipitation with respect to oxidation by O3/OH oxidation [4]. Simulations were also performed using an alternative anthropogenic emission scenario (based on AMAP/UNEP 2005), to see how the changes in European emissions influence the total amount of the mercury deposition flux. The comparison of these simulations show that although there is a large difference in anthropogenic emissions between the two reference inventories (2010 is around 30% less than 2005, over Europe), the total simulated deposition in the region diminishes only slightly (around 10%).