Modelling atmospheric mercury transport and deposition across Europe and the UK

There are inadequate measurements of surface ambient concentrations of merc ury species and their deposition rates for the UK deposition budget to be c haracterized. In order to estimate the overall mercury flux budget for the UK, a simple long-term ID Lagrangian trajectory model was constructed that treats emissions (1998), atmospheric transformation and deposition across E urope. The model, was used to simulate surface concentrations of mercury an d deposition across Europe at a resolution of 50 km x 50 km and across the UK at 20 km x 20 km. The model appeared to perform adequately when compared with the few available measurements, reproducing mean concentrations of el emental gaseous mercury at particular locations and the magnitude of region al gradients. The model showed that 68% of the UK's mercury emissions are e xported and 32% deposited within the UK. Of deposition to the UK, 25% origi nates from the Northern Hemisphere/global background, 41% from UK sources a nd 33% from other European countries. The total mercury deposition to the U K is in good agreement with other modelling, 9.9 tonne yr(-1) cf. 9.0 tonne yr(-1), for 1998. However, the attribution differs greatly from the result s of other coarser-scale modelling, which allocates 55% of the deposition t o the UK from UK sources, 4% from other European countries and 60% from the global background atmosphere. The model was found to be sensitive to the s peciation of emissions and the dry deposition velocity of elemental gaseous mercury. The uncertainties and deficiencies are discussed in terms of mode l parameterization and input data, and measurement data with which models c an be validated. There is an urgent requirement for measurements of removal terms, concentrations. and deposition with which models call be parameteri zed and validated. (C) 2001 Elsevier Science Ltd. All rights reserved.