The calculations for Iceland are different from the other countries because the high-resolution (1kmx1km) NordicWelfAir emissions was the first high-resolution emission inventory made and it has not been evaluated in detail yet. Therefore, only EMEP emissions (0.1° x 0.1° approx. 11 km x 6 km) are used in both DEHM and UBM for Iceland. The differences between the approach for handling emissions in DEHM and UBM include the distribution in the vertical, where DEHM has a vertical distribution profile depending on SNAP/GNFR category, whereas UBM does not. For the other Nordic countries, where NordicWelfAir emissions were available, the emissions from high stacks were given in separate point-source files, including the stack height, and this has been treated in a special way in UBM (plume-in-grid approach) to account for the vertical distribution. However, for Iceland these data are not available, and all emissions are gridded and emitted at surface level in the model.
Another issue with the Icelandic emissions is that the emissions from SNAP8 (national fishing fleet) has been reported (by Iceland) to EMEP with a geographic distribution, where all emissions occur in the harbours, not on the ocean. This is a choice made by the Icelandic emission authorities, but it means that the sources of SNAP8 emissions are placed very close to the population, as most of the Icelandic population lives close to the harbours and leading to an overestimation of concentration levels in these areas. It is not possible to adjust for this as it would require a redistribution of emissions based on the location of the fishing vessels that is beyond the scope of the present project.
Furthermore, Icelandic emissions of SOx are almost entirely dominated by hydrogen sulphite (H2S) emissions from geothermal power plants allocated to SNAP5. In these plants, hydrogen sulfide (H2S) is released during geothermal processing. In the atmosphere it is oxidized to SO2 and further to sulphate. The chemical lifetime for the chemical reactions that convert H2S to SO2 by OH radical is approx. two days and probably longer at Iceland due to the cold climate, so this H2S will not contribute to SO2, and definitely not to sulphate over Iceland. All H2S emissions are included in the SOx emission inventory as SO2 by assuming that one molecule H2S is equal one molecule SO2. In the first version of the air quality and health modelling it was assumed that SOx was 95% SO2 and 5% sulphate as is standard for combustion related SOx emissions. However, this led to very high modelled SO2 concentrations and also influenced estimates of PM2.5. After becoming aware of the hydrogen sulphide issue the air quality and health estimates were adjusted by post-processing. From the model runs for SNAP 5, 6 and 9 combined with the basic model run an estimate was made of the incorrect contribution from H2S emissions, which was reported as SO2 in the official emission inventory for Iceland and therefore treated as SO2 in the models system, to the concentrations of SO2, sulphate and nitrate by assuming that 100% of the contributions from SNAP5, 6 and 9 to these three compounds are coming from H2S emissions and with this assumption it is possible to adjust all model results.
The NordicWelfAir emissions available for Norway for this project, was not complete for the SNAP sectors 1, 3, 4, 5, 8 and 9. Therefore, it was decided to use EMEP GNFR sectors for Norway instead for these specific emission sectors. It should be noted, that the EMEP data are similar, but with a more coarse spatial resolution, compared with the NordicWelfAir data.
In Figure 5.6–5.8 the total emissions of selected pollutants (SOx, NOx and PM2.5) are shown for the Nordic countries for the aggregated SNAP sectors for 2019 and 2030.
The combined sectors of SNAP1 (Energy), SNAP3 (Industrial combustion) and SNAP4 (Industrial processes) are the emission sectors that contribute the most to SOx except for Iceland, where the combined sector of SNAP5 (Extraction etc,), 6 (Solvents) and 9 (Waste) show the largest contributions to SOx emissions due to geothermal energy production allocated to SNAP5. The largest source of SOx is from geothermal power plants, and SOx emissions are therefore dominated by hydrogen sulphide emissions.
SNAP7 (Road transport) contributes the most to NOx in 2019 but decreases towards 2030 where other sectors also contribute significantly. SNAP8 (off-road) also contributes significantly to NOx. For Iceland these emissions are dominated by fishing vessels. They are not geographically correct distributed in the EMEP emission inventory as all emission are allocated to harbour areas and not where most of the emissions take place at sea.
SNAP2 (Residential combustion) represents almost entirely emissions from wood burning in wood stoves in Nordic countries and contributes the most to PM2.5 emissions except for Iceland since woodstoves are not commonly used in Iceland.
There is a reduction for all countries and pollutants from 2019 to 2030.