Sensitivity studies and evaluation of the Volatility Basis-Set Approach within the LOTOS – EUROS Model in Europe 2011 / Gutachter: Prof. Dr. Peter J. H. Builtjes PD Dr. Peter Névir / Supervisor: Dr. Astrid M. M. Manders
Anne Sophie Walter / Masterarbeit – 2014
In this study the "volatility basis set" (VBS) approach which has been implemented in the Dutch LOTOS-EUROS model is evaluated. For this purpose the concentrations of organic and elemental carbon (OC and EC) are used for twelve different stations in Germany and the Netherlands. These differ both in their situation and in their classification and therefore provide a good overview of the quality of the model results. The LOTOS-EUROS model is a regional operational 3d chemistry transport model with a res-olution of 0.5° x 0.25° covering the whole of Europe. The herein implemented VBS approach takes into account the volatility of the aerosols and makes it possible for them to change their state of aggregation between the gas phase and the aerosol phase. This was not possible with the previous modeling method. The aim of this study is thus to evaluate the VBS approach used in the LOTOS-EUROS model, to identify problems and evaluate solutions. For this purpose seven sensitivity studies are carried out to. The results show that using the VBS approach leads to higher modelled OC concentrations, which lead to an overestimation of the measured values in summer and in an underestimation in winter. However, the time series for the OC concentrations of the VBS approach show higher variability than the time series without this approach. So the VBS approach should be improved before it can be used, thus an attempt is made to develop improvements using sensitivity studies. Advancements can be achieved by using a combi-nation of four of these improvements. Here, the most successful sensitivity changed are summarized in one final model run. The results show improvements of the model results compared to a model run without VBS approach and a model run with the unchanged VBS approach. The use of the changed VBS approach gives an increase of the correlations for the OC concentrations in Melpitz from 0.0001, for the run with unchanged VBS approach, to 0.0010, for the final run. So the correlations are now 10 times higher than for the default run. The very low correlations can also be found for the other German stations. For the four used Dutch stations higher correlations are determined. The correlation for the final run (0.3615) almost doubled with respect to the default run of (0.1735). Again, these are not high correlations, but they are significantly higher than for all German stations. Therefore, it should be verified in further studies whether the Dutch LOTOS-EUROS model has problems with the modeling of OC and EC concentrations over Germany. The conclusion is that using the VBS approach with the modifications proposed here leads to improved results in comparison to runs without the VBS approach. As with these changes there are lower OC concentrations modeled in summer and higher concentrations in winter which agrees better with the measurements.