Aarhus Universitets segl

No. 677: Modelling of dioxin deposition in Denmark

Hansen, K. M.; 2008. Danmarks Miljøundersøgelser, Aarhus Universitet. NERI Technical Report.

 

Summary

We have estimated the deposition of dioxin in Denmark for the years 1970, 1975, 1980, 1985, 1990, 1995, 2000 and 2004 as well as the contribution to air concentrations and depositions from Danish sources relative to the contribution from other European sources. The estimate is based on model simulations with the high-resolution atmospheric chemistry-transport model DEHM, where dioxin is modelled as one compound in form of particles. Two different expert emission estimates from EMEP’s Meteorological Synthesizing Centre East were used as model input. There are large differences in estimated emissions for some countries from 1990 and onwards, which has a large influence on the simulated depositions. However, it has not been possible to determine which estimate is the most realistic.

 

The concentrations of dioxin in air as well as the depositions increase slightly up to 1980, from where they decrease until 2004. The simulated air concentrations in 2004 are 3,2 fg I-TEQ/m3 and 0,8 fg I-TEQ/m3 for the two emission estimates. The deposited amount of dioxin to Danish land surfaces are 36 g I-TEQ and 9 g I-TEQ for the two emission estimates for 2004.

 

The relative contribution from Danish sources to the deposition of dioxin to Danish land surfaces are 14% and 15% for the two emission estimates for 2004. Despite of large differences in emissions and simulated air concentrations and depositions between the two applied emission estimates, the relative contribution of the Danish sources to the deposition in Denmark does not differ much between the two emission estimates. The contribution of Danish sources to the deposition to Danish land surfaces is estimated to be between 10% and 20%, although there is a large regional variation, from less than 5% to more than 40%. It should be kept in mind that there are sources that are not included in this estimate, such as sources outside Europe and re-emission from previously deposited dioxin, which potentially can give a large contribution to the deposition.

 

It is difficult to determine how trustworthy the model results are, partly because the applied model set-up was simplified and partly due to the large uncertainties on the applied emission estimates. Finally the simulated concentrations and depositions are not in accordance with previously made Danish measurements. The simulated air concentrations are one order of magnitude lower than the measured air concentrations, while the simulated depositions are also lower, but of the same order of magnitude as the deposition estimated from measurements. The difference between simulated and measured concentrations and depositions could indicate either that the model set-up is not adequate, that there are sources not included in the emission estimates, or that the included sources in the emission estimates are too low. It is interesting to notice that the difference between simulated and measured depositions is smaller than the difference between simulated and measured air concentrations.

 

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