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The most prominent cause of climate change is the anthropogenic emission of greenhouse gases. Methane (CH4) is the second most important greenhouse gas, after carbon dioxide (CO2). Enhanced methane concentrations account for 23% of the anthropogenic radiative forcing. Agriculture and fossil fuel exploitation are the largest emission sources for methane . Given that methane emissions play such an important role in climate change, this study seeks to contribute to the insights in the methane emission in the Netherlands. Model simulations are a very important tool in gaining insights in methane emissions. This study uses the WRF-Chem model to conduct simulations of CH44 concentrations in the Netherlands. The aim of this study is to test the quality of high resolution simulations of methane concentration. An emission inventory by the RIVM, with a resolution of 1 km x 1 km is used as input in the WRF-Chem model. This model is used to conduct high resolution simulations of the methane concentration, with a grid size of 3 km x 3 km, on the domain of the Netherlands. The emissions from the inventory were used as input for 13 individual tracers, one for every emission subgroup in the inventory. To test the quality of these simulations, the results are compared with in situ measurements of methane concentration. These continuous measurements are from two locations in the Netherlands, Lutjewad and Cabauw. The analysis showed an underestimation of the simulated CH4 concentration compared to the observed CH4 concentration, during peak events. This underestimation is likely the result of the emissions being averaged on grids of an area of 3 km x 3 km. This averaging of emissions results in a poor representation of plume emissions in the simulations. Therefore local accumulation of CH4 during peak events is possibly less in the simulations. Further analyses of the simulation output showed a large discrepancy between observations and simulations, in the diurnal range of methane concentration. The observed diurnal range is 3 to 4 times larger in Lutjewad and Cabauw than the diurnal range in the simulated CH4 concentration. Differences in boundary layer height, between observations and simulation, were not of the same order as for the methane concentrations. Furthermore, implementing diurnal variability in several emission sources did not improve the diurnal range in the simulated methane concentration. In the final part of the analysis it is shown what the influence of the wind direction on the magnitude of the excess methane concentration per tracer is. The simulations underestimate the dependence of the excess methane concentration on the wind direction. This can again be caused by the bad representation of plume emission in the simulation. Another cause could be underestimated methane emissions around the measurement sites. The WRF-Chem simulations showed differences in the magnitude of the variability of methane concentration on several timescales. Further research on the discrepancies in simulated and observed variability in CH4 concentrations is needed before WRF-Chem can be used for research on high resolution simulations of CH4 emission in the Netherlands.

Supervisors: Guus Velders, Thomas Roeckmann