This report presents results from a methodological study on how to calculate and interpolate the time series of carbon stock changes in the fine litter and soil organic carbon pools on forest land remaining forest land and grassland remaining grassland for reporting of the LULUCF sector in the annual greenhouse gas inventory submitted to the UNFCCC and the EU.

Since rather small variations along the time series estimated by the present calculation and interpolation method results in huge national variations in sinks or sources of CO₂ at the national level, there has been a wish to find an alternative way of calculating the time series that reduces the effect of recalculations between submission years. The aim of the project was to evaluate alternative calculation methods for the time series for changes in the litter and soil carbon pools. The ambition is that the new method should result in time series that are as close as possible to the long-term trends in litter and soil carbon pool change by reducing the effect of random variation and interpolation methods within and between the submissions. The changes should be calculated so that the reporting is still representing carbon pool changes based on repeated measurements on the permanent plots of the Swedish Forest Soil Inventory.

Two different calculation methods were tested and compared with the method used up to submission 2022. The “average change method” estimates the average annual change for each plot over the whole time series instead of between each measured occasion. This results in a time series at plot level with no variations. However, when changes from all plots are averaged for each year in the time series some variation is introduced due to that plots may enter or leave the time series due to land-use change. For forest land remaining forest land, the method worked best and it significantly reduced variation along the time series and inter annual variation was also reduced compared to the previous method. The method was less effective on grassland remaining grassland where the large proportion of plots involved in land-use change contributed significantly to time series variation. The total aggregated carbon pool changes over the whole time series for this method is identical with the method that has been used up to submission 2022. 

The second method tested is based on regression of the carbon pool over the entire time series instead of estimating change on each inventory plot by repeated measurement. This method essentially leads to a total elimination of the variation over the reported time series but the difference between different submissions were more substantial. The aggregated amount of reported changes differ a lot from the other methods.

The conclusion from this project is to recommend the average change method to be used for calculating and interpolating the time series for fine litter and soil organic carbon for forest remaining forest and grassland remaining grassland.

This report summarizes the development work carried out in five different studies between 2017 and 2021 aiming to improve emission calculations for small-scale biomass combustion in the Other sector (CRF/NFR 1A4) for reporting to the UNFCCC and the CLRTAP. The most important measures include a more detailed and transparent structure of activity data as well as updated emission factors for different biofuels and heating technologies. Reports and documentation from earlier studies are attached.

Sweden’s emissions of greenhouse gases and air pollutants from stationary combustion, reported to among others UNFCC and CLRTAP, are in most cases calculated from fuel amounts and calorific values from Swedish energy statistics, and emission factors developed by SMED.

During autumn 2021 and spring 2022, several projects with the purpose to revise and update certain emission factors for stationary combustion have been conducted. The results on these projects (UF-27 Updates of certain emissions factors for stationary combustion, UF-31 Revision of certain emission factors for stationary combustion – stage 2 and parts of UF-07 Updates of emission factors for pulp and paper industry NFR 2H1) have been summarized in the current report.

The most significant effect of the revision of emission factors is seen for emissions of dioxin in NFR 1A1 and 1A2, where the annual average decrease would account to 65 % and 80%, respectively. Large effects are also seen for emissions of N₂O in CRF 1A4, where the average decrease was 35 %, and for NH₃ emissions in NFR 1A1 with an average increase of 10 %. Certain effects on the biogenic CO₂ emissions are also seen, with an average increase of 6 % to 9 % in NFR 1A1, 1A2 and 1A4. Emissions of SO₂ decrease on average with 3 % to 8 % for NFR 1A1, 1A2 and 1A4, while corresponding decrease for CO was between 4 % and 6% for the same NFR codes. Zink emissions in NFR 1A1 had an average decrease of 5 %. The effect on other emissions is relatively small, under ±5 % in average change of emissions. 

As a result of the projects UF-27, UF-31 and parts of UF-07 the following revisions are proposed:

• Emissions factor for biogenic CO₂ from combustion of black liquor from 96 kg/GJ is suggested to be 105 kg/GJ,
• Revisions of emission factors for CO₂ and wood fuels, pine and pitch oil and other biomass within stationary combustion (CRF/NFR 1A1, 1A3, and 1A4),
• Emission factor for dioxin from combustion of wood fuels, peat and other biomass is suggested to be revised,
• Emission factors for other fuel categories are suggested to be revised,
• All recommendations of revised emission factors with the reference of “SEPA 1995”,
• Revision of emission factors updated in the EMEP/EEA Guidebook 2019.