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 PM 1 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 PM 1 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 SO 4 2− , making this hotspot more comparable to those observed in other global hotspots than to typical European urban backgrounds.