BC is a short-lived climate forcer and an air pollutant that contributes to both warming and public health impacts. It is produced from the incomplete combustion of fossil fuels and biomass, with major sources including residential heating (especially wood burning), road transport, industrial processes, and open biomass burning. Although BC is not specifically regulated under the Paris Agreement, its co-emission with greenhouse gases and its strong warming potential—second only to CO₂—make it relevant to climate mitigation strategies. Accurate estimates of BC emissions are necessary to quantify its contribution to radiative forcing and to reduce uncertainties in its overall climate impact.

To estimate BC emissions, the projects used harmonised concentration measurements from the ACTRIS and EMEP networks, processed through the FLEXPART-FLEXINVERT modelling system. Prior emissions were derived from three inventories: ECLIPSE v6b, the LRTAP baseline, and EDGAR HTAP v3. As these inventories generally exclude wildfire emissions, additional data from the CAMS Global Fire Assimilation System (GFAS) for 2022 were included. To avoid double counting, emissions from agricultural waste burning (AWB) were excluded where appropriate. The dataset incorporates measurements from 14 sites distributed across Europe. These stations were selected to reflect a range of geographical and emission contexts, including Arctic, rural, and urban settings. Examples include Zeppelin in Norway (remote Arctic), Hyltemossa in Sweden (rural background), and sites in Rome and Dublin (urban environments). Emissions were estimated on a 0.1° x 0.1° grid, using sectoral classifications consistent with the SNAP system. National expert inventories were used, where available, to cross-check key sectors such as residential combustion and transport. Attention was given to common sources of uncertainty, such as limited sectoral coverage, differences in estimation methods, and spatial or temporal inconsistencies across inventories.

The modelling results confirmed the expected seasonal variation in BC emissions, with higher values during winter and lower emissions during summer. An exception was observed in March 2022, when emissions increased markedly across parts of east-central Europe, particularly in Austria, Poland, and Germany. This increase is consistent with elevated wildfire activity during the spring fire season, as documented in the annual European fire report (San-Miguel-Ayanz et al., 2022). Concurrently, the escalation of the conflict in Ukraine in early 2022 affected energy consumption patterns in Europe. Several countries increased their use of coal and biomass, which may have contributed to the observed rise in BC emissions. For example, in March 2022, brown coal usage in Germany and Poland was up to 34.4% higher compared to other months, and petroleum product use in Austria and Italy increased by up to 22.7%. The study also highlights regional differences in emission patterns. The largest contributors to total BC emissions in 2022 were Poland, France, Italy, Spain, and Great Britain. Differences between bottom-up inventories and inverse estimates were most pronounced in parts of southern and eastern Europe. In several cases, EDGAR-based estimates diverged from national inventories, indicating areas where further reconciliation may be needed. A methodological advancement in this work was the implementation of a log-normal error distribution for prior flux errors within the FLEXINVERT inversion system. This distribution better reflects the statistical properties of emission sources such as BC, ensures non-negative posterior values, and supports more realistic uncertainty quantification.

The results illustrate the potential of inverse modelling to improve the spatial and temporal accuracy of emission estimates. They also demonstrate the importance of integrating harmonised observational data with up-to-date bottom-up inventories. In certain regions, such as Great Britain, the study found that existing inventories may underestimate BC emissions, suggesting the need for further refinement. The emission estimates for Ireland and Italy will be made available to national inventory compilers working within the framework of the UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP). The results are also expected to inform the European synthesis report under EYE-CLIMA and may contribute to national inventory annexes under the United Nations Framework Convention on Climate Change (UNFCCC). While the estimates presented are preliminary, they provide a valuable foundation for future work. The next steps include validation through further atmospheric modelling and inversion studies, as well as continued collaboration with national experts to integrate independent scientific assessments into official reporting frameworks.

In summary, this joint effort by PARIS and EYE-CLIMA contributes to a more comprehensive understanding of Black Carbon emissions in Europe. By combining observation-informed top-down modelling with existing inventory approaches, the work supports ongoing efforts to enhance the consistency, accuracy, and policy relevance of emission estimates across the continent.