EMEP GRID - comparisons
To compare emissions from the new 0.1°x0.1° (long-lat) gridding system with gridded 50x50km² PS data or data from other models (like MACC or IISSA ECLIPSE) there are challenges related to differences in grid resolution, projection and category definitions.
The figure shows the 50x50km² PS grid and the 0.1°x0.1° long-lat grid at local scale. The extent is located at the boarder of Austria, Slovakia and Hungary respectively and shows no matching between the grid systems. Therefore for comparison a workflow is needed.
Comparison of 50x50km² and 0.1°x0.1° grid data
The objective of this approach is to compare the new 0.1°x0.1° long-lat grid from the new gridding system with the 50x50km² PS grid from the old system. In a first step the national total emissions from each pollutant in the 0.1°x0.1° grid are added up to the 50x50km² grid. Afterwards a set of visualisations is generated, which shows the old and the new source with visualised differences in 50x50km² resolution.
As database the gridded National Total (NT) emissions of all available pollutants (CO, NH3, NMVOC, SOx, NOx, PM10, PM2.5 and PMcoarse) for the year 2014 - gridded in 2016- was taken.
The tasks are processed with Microsoft Access and ESRI ArcGIS 10.2.
The base projection of all datasets is the projection of the 50x50km² grid, which correspond to the Lambert azimuthal equal-area projection of the EEA reference grid (ETRS_1989_LAEA_52_N_10E; EPSG 3035). Therefore the data of the 0.1x0.1 grid had to be transformed.
In a first step all data is loaded into an access database where the emission values are aggregated to the grid cell. (National borders were not considered). The table is joined to the grid which contains the area values.
Through an identity function the two grids are overlaid in ArcGIS.
In a next step the area of each polygon is calculated. This value represents the fraction to weight the correct amount of emission to the corresponding grid cell. Afterwards the emissions are summed up to the 50x50km² grid cell. To visualize the deviation the absolute value of the gap is calculated.
The output of the results are visualised in three different maps. The map with aggregated values from the 0.1°x0.1° grid shows the whole EMEP Domain. The original map of the old 50x50km² grid is visualised the same way and has the same classification system.
The third map shows the deviation of each grid cell to highlight the differences between these two methods. The deviation map is classified by standard deviation.
For further information an extract from the classification is prepared (“deviation legend”) for each pollutant. This legend shows the values at the deviation classes.
Direct comparison is made in the maps of so called “expert view”. The maps show enlarged subareas simultaneously in 50x50km² grid original on the left hand side and the aggregated 0.1°x0.1° grid on the right. Additional information such as country info, large point sources and absolute pixel values are shown. Absolute pixel value is only shown, if the standard deviation of the compared grid lays 0.5 or above.
To navigate in the expert view maps a map with a subarea overview is provided (Expert view sheet lines). The number of the subarea corresponds to the number in the header on the right hand side of the expert view maps.
The subarea overview map and the "expert view" documents with comparison maps for each pollutant can be downloaded from the right column of this page.
Here you can download the so called “expert view” comparison maps for 2014 which shows enlarged subareas of the EMEP domain simultaneously in the original 50x50km² and the aggregated 0.1°x0.1° grid.
The comparison maps for 2014 are currently revised and will be available soon.
To navigate in the expert view maps a map with a subarea overview is provided. The number of the sheets is corresponding to the number in the file name of the expert view maps.