The pulp and paper industry, and in particular the kraft (sulpahte) pulp production, is an important source of several short-lived climate forcers (SLCFs), including nitrogen oxides (NOₓ), sulfur dioxide (SO₂) and particulate matter (PM). Reliable emission factors are essential for national emission inventories and for international reporting under frameworks such as the EU National Emission Ceilings Directive (NECD) and the Convention on Long-Range Transboundary Air Pollution (CLRTAP). However, several internationally used emission factors for the sector are based on older datasets and may therefore not fully reflect the emission performance of modern pulp mills.
Sweden and Finland are among the world's leading producers of kraft pulp and are subject to the EU Industrial Emissions Directive (IED), which requires continuous or periodic monitoring of key air pollutants and the application of Best Available Techniques (BAT). Consequently, the Nordic kraft pulp sector provides a unique source of high-quality emissions data covering more than three decades of technological development and emission reductions.
The primary aim of this study is to develop updated emission factors for NOₓ, SO₂ and total suspended particles (TSP) from kraft pulp production in Sweden and Finland. The study also evaluates these emission factors against international reference values presented in the EMEP/EEA Air Pollutant Emission Inventory Guidebook 2023 and in the 2000 and 2015 Best Available Techniques Reference Documents (BREFs) for the pulp and paper industry. The two BREF versions were included to enable comparison with both the aggregated process-level emission factors presented in the 2000 BREF and the reported emission data and the more detailed process-specific BAT-associated emission factors presented in the 2015 revision, thereby providing insight into how emission performance and BAT reference levels have evolved over time.
Detailed facility reported emission data from kraft pulp mills were compiled for the period 1990–2023, together with activity data expressed as annual production of air-dry pulp (ADt). National and plant-and-process unit implied emission factors were calculated as production-weighted averages. Recovery boilers account for the majority of NOₓ and TSP emissions, whereas diffuse process emissions is the most important source of sulfur emissions.
The results show that Swedish and Finnish kraft pulp mills display similar emission performance, particularly in recent years, reflecting comparable abatement technologies, regulatory frameworks and operational practices. The average national aggregated emission factors for the period 2019–2023 were 1.25–1.44 kg NOₓ/ADt, 0.15–0.28 kg SO₂/ADt and 0.22 kg TSP/ADt. The plant- and process unit-specific analysis further shows that most Nordic kraft pulp mills operate within current BAT-associated emission factors.
For NOₓ, the recent national emission factors generally fall within the BAT range reported in the 2000 BREF and are broadly consistent with plant-level observations reported in the 2015 BREF. Emission factor levels have remained relatively stable over time, indicating that currently applied combustion optimisation measures might provide limited potential for further reductions without the implementation of more advanced abatement technologies.
In contrast, SO₂ and TSP national emission factors are generally close to or below the lower BAT levels reported in the 2000 BREF. Together with plant-level observations and BAT factor ranges presented in the 2015 BREF, these results indicate substantial reductions in sulfur and particulate emissions over recent decades. The reductions are primarily associated with the widespread implementation of scrubbers, electrostatic precipitators, cyclons, and improved collection and combustion of internal process gases.
The comparison with the EMEP/EEA Guidebook default emission factors (Tier 2) reveals systematic differences to the emission factors observed in Nordic kraft pulp mills. Guidebook emission factors for SO₂ and TSP are substantially higher than the emission factors derived in this study and appear more representative of Nordic emission factor levels observed during the early 1990s. Conversely, the Guidebook emission factor for NOₓ is lower than the observed Nordic emission factors and may therefore underestimate current emissions from modern kraft pulp production. The analysis also indicates that the methodological basis and system boundaries used to derive some Guidebook emission factors are not always fully transparent, particularly regarding the translation of BAT-associated emission factors into default emission factors.
Overall, the results demonstrate the value of using detailed plant-level emission data to develop representative and time-dependent emission factors for the pulp and paper industry. The updated emission factors presented in this study provide a more accurate representation of historical trends and current emission performance in modern Nordic kraft pulp mills and may support future revisions of the EMEP/EEA Guidebook as well as the ongoing Intergovernmental Panel on Climate Change (IPCC) methodological work on emission inventories for SLCFs.