AbstractsGeography &GIS

The modelling of terrain in chemical transport models is a difficult task. Most models have a too coarse resolution to be able to resolve regions with more complex terrain. Problems arise when validation of the models needs to be done with measurements from different stations at different altitudes. The largest deviation is found at stations with a high altitude above sea level in regions with strong altitude variations. This problem has been identified within the the chemical transport model, EMEP MSC-W which is a global air quality model developed for European conditions. The aim of this thesis is to analyse and post-process 3D data from the EMEP MSC-W model in order to create a sub-grid model that captures the topographic effects in a better way. This will be done for three different pollutants, ozone, nitrogen dioxide, sulphur dioxide and sulphate. The sub-grid model scales the output data from EMEP MSC-W from 50x50 km to 1x1 km and extracts data using four different methodologies. Two of the methods are based on altitude above sea level or absolute altitude and one is on a relative altitude. This relative altitude is defined by subtracting the lowest altitude within a search radius of 3, 5 or 10 km, from a given location. These methods are compared with the output data closest to the model topography and validated with measurements. The model is developed and evaluated with the diurnal variations of ozone and tested for nitrogen dioxide, sulphur dioxide and sulphate. Other possible developments of this model will also be discussed regarding downscaling of dry deposition with respect to land use, temperature and pressure. The results became different for all the pollutants, but since there are far more measurement stations for ozone the statistical significance of this result becomes important. The best method of extraction was when using the relative height with a search radius od 3 km. A downscaling of the land use, temperature and pressure also points out the possibilities of getting improvements if implementing a higher resolved dry deposition.