Sarajevo severe fine aerosol burden: A European pollution hotspot

Sarajevo is the most PM_2.5-polluted European capital (IQAir Report, 2024); however, fine aerosol measurements' studies in the city are scarce. This study presents the results of an 8-month campaign in Sarajevo site focusing on organic aerosol (OA) and equivalent black carbon (eBC) and their respective sources. The mean PM₁ campaign concentration in Sarajevo is 34.2 μg·m^-3 with significantly higher contributions in winter stagnation episodes during which daily concentrations can exceed 100 μg·m^-3. Furthermore, the number of daily PM₁ concentrations during this 8-month campaign exceeding the EU legislation PM_2.5 limit value are more than 4 times the stated maximum number of days per year. The eBC sources consist of liquid fuel (eBC_lf, 62%), and solid fuel (eBC_sf, 38%) combustion, the latter proportion being higher than in other European sites. OA source apportionment results revealed 4 factors: hydrocarbon-like OA (HOA, 15%), two solid fuel combustion OA (SFOA1, 31%; SFOA2, 9%), and oxygenated OA (OOA, 44%). HOA and eBC_lf are related to traffic emissions; SFOA1, SFOA2, and eBC_sf are associated with residential heating, although SFOA2 potentially reflects additional regional combustion sources; and OOA shows regional, secondary aerosol characteristics with biomass burning emissions influence. Accordingly, Sarajevo's burden from air pollution could lead to all-cause mortality on the order of 10% during its heavy-polluted episodes. Overall, the submicron aerosol in Sarajevo constitutes a hotspot of fine aerosol pollution in comparison to other European sites both in its absolute concentrations and its relative proportion of biomass burning and SO₄^2-, making this hotspot more comparable to those observed in other global hotspots than to typical European urban backgrounds.