Road-traffic emissions of ultrafine particles and elemental black carbon in six Northern European cities

• Study probes UFP and eBC emissions in Lithuania's six major cities. • Panevėžys and Vilnius show highest eBC; Alytus lowest. • Diesel prevalence and fleet age drive elevated UFP and eBC in Panevėžys. • Adapted OSPM model derives emission factors from mobile measurements. • Findings aid air quality policy and sustainable mobility strategies. Urban air pollution from vehicular emissions remains a pressing public health concern, particularly in Eastern Europe, where data gaps hinder effective mitigation. This study, conducted in the summer of 2024, presents the first detailed analysis of ultrafine particle (UFP) and equivalent black carbon (eBC) emissions from road traffic across Lithuania’s six major cities: Vilnius, Kaunas, Klaipėda, Šiauliai, Panevėžys, and Alytus. We used a custom mobile laboratory to capture real-world emissions, revealing stark spatial disparities. Panevėžys and Vilnius topped eBC levels (10400 ng/m³ and 10200 ng/m³, respectively), driven by aging vehicle fleets and a diesel prevalence of 70 % in Panevėžys, which also recorded the highest UFP concentration (97800 particles/cm³). Emission factors, calculated using an adapted Operational Street Pollution Model (OSPM), identified Vilnius’ light-duty vehicles as leading in particle number emissions (8.90 × 10¹⁴ particles/(km·veh)), likely due to the prevalence of gasoline direct injection engines. At the same time, Panevėžys dominated eBC emissions (150 mg/(km·veh). Heavy-duty vehicles, including buses and trucks, exhibited emission factors up to five times higher than those of their light-duty counterparts, thereby amplifying their impact in urban areas. These findings illuminate emission dynamics in an understudied region, providing policymakers with precise and actionable insights for targeted interventions, such as fleet upgrades or the establishment of low-emission zones. By addressing a critical knowledge gap, this study empowers the scientific community and public health advocates to devise strategies that combat vehicle-related pollution, reduce exposure to harmful pollutants, and foster healthier urban environments across Eastern Europe and beyond.