Influence of Europe’s Shifting Energy Conditions on the Temporal Variability and Interannual Changes in Equivalent Black Carbon (eBC) in Kraków, Poland

Equivalent black carbon (eBC) is a key component of fine particulate matter PM2.5, originating from incomplete combustion processes and exerting significant impacts on air quality, human health, and climate. This study investigates the temporal variability and interannual changes in eBC in Kraków, Poland, in the context of Europe’s recent energy policy changes and ongoing energy transition. A one-year dataset (October 2023 to September 2024) based on multi-wavelength optical measurements was analysed to quantify total eBC and its fossil-fuel (eBC) and biomass-burning (eBCbb) components and compared with 2020–2021 observations. Results show strong seasonal variability, with winter eBC concentrations averaging 4.0 µg m−3 and peaking at 5.5 µg m−3 in February, while summer minima reached 1.2–1.5 µg m−3. Biomass-burning contributions remained low throughout the year, ranging from 0.1–0.2 µg m−3 in summer to 0.4–0.5 µg m−3 in winter. PM2.5 concentrations followed similar trends, with winter values of 24–31 µg m−3 and summer levels of 8–12 µg m−3. Extreme pollution episodes were observed during winter, with PM2.5 exceeding 120 µg m−3 and eBC reaching 13 µg m−3. Despite the 2019 ban on coal and wood combustion, elevated wintertime eBC indicates a strong influence of regional emissions transported from surrounding areas. A clear weekly pattern was identified, with eBC concentrations approximately 40% higher on weekdays (3.1 µg m−3) compared to weekends (2.2 µg m−3), while eBCbb showed minimal variation. The winter-to-summer eBC ratio (2.2) highlights the combined effects of heating demand and meteorological conditions. The findings demonstrate that the energy policy changes intensified winter pollution variability and weather events rather than increasing annual averages. The observed differences indicate that pronounced wintertime variability and episodic pollution remained important during 2023–2024 despite lower annual mean concentrations than in 2020–2021. While local policies effectively limit direct emissions within Kraków, regional contributions remain significant, emphasizing the need for coordinated emission reduction strategies and the inclusion of episodic extremes in air quality and health impact assessments.