The research, led by Bojana Petrović of the Vinča Institute of Nuclear Sciences at the University of Belgrade, together with colleagues from Spain’s Institute of Environmental Assessment and Water Research and the Norwegian Institute for Air Research, was conducted at an urban background site called Ada Marina, located on Ada Ciganlija, Belgrade’s largest recreational area along the Sava River. From June 2023 to May 2024, the team collected daily filter samples using three co-located low-volume samplers, yielding 84 representative PM10 samples for analysis. What set this campaign, dubbed WeBaSOOP, apart from earlier work in the region was its unprecedented chemical scope: rather than measuring only elements or ions, the researchers quantified 34 species, including organic and elemental carbon, 27 elements, four major ions, and — for the first time in Serbia and the wider Western Balkans — a suite of specific organic tracer molecules.

These tracers are the forensic key to the study. Levoglucosan, mannosan and galactosan are anhydrosugars released when cellulose burns, making them unambiguous fingerprints of biomass combustion. Sugars and sugar alcohols such as glucose, mannitol and arabitol mark primary biological aerosol particles — fungal spores, pollen, plant fragments and microbial debris. Two-methyltetrols, meanwhile, are oxidation products of isoprene, a volatile organic compound emitted in abundance by vegetation, and serve as markers of biogenic secondary organic aerosol. Feeding this rich chemical inventory into the United States Environmental Protection Agency’s Positive Matrix Factorization model, version 5.0, the team resolved the PM10 mass into seven factors, each with a distinct chemical profile, seasonal rhythm and wind-direction signature.

The dominant factor was biomass burning, contributing 21 percent of PM10 mass annually and a striking 34 percent during the heating season from October to April. Its profile was anchored by 80 percent of total galactosan, 79 percent of mannosan and 76 percent of levoglucosan, alongside roughly half of the potassium and chloride and a third of the organic carbon. Diagnostic ratios — an organic carbon to elemental carbon ratio of 9.4 and an organic carbon to levoglucosan ratio of 8.3 — matched values reported for wood smoke across Europe. The seasonal peak aligns with a well-known reality in Belgrade: an estimated 300,000 households are not connected to the district heating network and rely largely on wood as their heating fuel. During cold spells, temperature inversions trap these emissions in a stable near-surface layer, allowing pollutants to accumulate unchecked.

Intriguingly, the study also caught biomass burning outside the official heating season. On 2 October, before heating officially begins on 15 October and with ambient temperatures around 15 degrees Celsius, concentrations of the anhydrosugar tracers spiked sharply. The ratio of levoglucosan to mannosan, which distinguishes softwood burning (ratios below about 4) from hardwood burning (around 14 to 15), averaged 8.9 for the burning factor overall but reached 18.9 in summer versus 8.0 in winter. Satellite observations confirmed active fires in Vojvodina on that October day, pointing to agricultural waste burning — a phenomenon documented in Serbia every October since 2000 — while summer contributions may also reflect charcoal combustion at the restaurants dotting the Ada Ciganlija lakeside near the monitoring site.

The second-largest source, at 18 percent, was ammonium sulphate, a secondary aerosol formed when sulphur dioxide is oxidised in the atmosphere and neutralised by ammonia. This factor carried 55 percent of total ammonium and 54 percent of sulphate, with the coexistence of ammonium bisulphate and ammonium sulphate indicating only partial neutralisation of sulphuric acid. Its high organic-to-elemental carbon ratio of 9.1 confirmed the aged, regional character of these particles. Wind analyses pointed to influences from the south and southeast, consistent with transport from the coal-fired Nikola Tesla and Kolubara thermal power plants located 25 and 50 kilometres from the city, and the Kostolac plant 60 kilometres to the east. Notably, the 2024 launch of flue gas desulphurisation at Nikola Tesla A may already be reshaping this contribution.

Mineral dust ranked third at 17 percent, characterised by crustal elements — aluminium, titanium, strontium, magnesium and calcium — and showing influence from the southwest. The campaign captured a Saharan dust outbreak on 31 March 2024, confirmed by sodium-to-aluminium and potassium-to-aluminium ratios closely matching literature values for Saharan material, and corroborated by FLEXPART footprint modelling that traced air masses back across the Sahara. But dust was not purely natural: preparatory construction for the future Belgrade metro depot at Makiš, roughly seven kilometres upwind, left its imprint on the factor’s wind polar plots, blending local construction dust with long-range transported soil.

Perhaps the most novel finding concerns the biological fraction. Two factors of biogenic origin — primary biological aerosol particles and biogenic secondary organic aerosol from isoprene — together accounted for 20 percent of PM10 mass, each contributing 10 percent. The primary biological factor, traced by sugars and sugar alcohols, peaked in the warm months and showed influence from the vegetation of Ada Ciganlija and the Košutnjak forest three kilometres away. Using the mannitol-to-arabitol ratio of 1.0, consistent with fungal spore signatures across Europe, the team estimated that 21 to 44 percent of the organic carbon in this factor derives from fungal spores. The isoprene-derived secondary factor, marked by 2-methylerythritol and 2-methylthreitol, appeared exclusively during the growing season and peaked in summer, its co-occurrence with sulphate species suggesting acid-catalysed aqueous-phase formation — a mechanism first proposed in a landmark 2004 Science paper.

The remaining sources were a mixed traffic-and-industry factor at 15 percent, blending exhaust and brake-wear tracers such as iron, antimony, copper and tin with industrial markers including arsenic, cadmium, lead and vanadium, and a smaller 9 percent factor combining aged sea salt transported from the Atlantic with road salting and local combustion emissions. Mass reconstruction independently confirmed the source apportionment: the carbonaceous fraction dominated PM10 composition at 54 percent annually, followed by secondary inorganic aerosol at 19 percent and mineral dust at 13 percent. The average PM10 concentration over the campaign was 23.9 micrograms per cubic metre — compliant with the current EU limit of 40 but exceeding both the 20 microgram limit that the new EU directive will impose from 2030 and the World Health Organization’s 2021 guideline of 15 micrograms. Winter concentrations of 28 micrograms far outstripped summer’s 19, and the daily limit was breached four times, peaking at 92 micrograms on 19 December.

The implications reach well beyond Belgrade. Because roughly a fifth of the particulate mass originates from biogenic sources that no emission control can touch, and mineral dust adds another irreducible background of around 4 micrograms per cubic metre, meeting future air quality standards will demand disproportionately deep cuts in controllable anthropogenic emissions. The study’s authors argue that targeted mitigation of residential wood burning — the largest single controllable source — offers the clearest path forward, while the identification of biogenic factors for the first time in the region provides a scientific basis for the kind of natural-source accounting that emerging legislation may eventually permit. As Europe tightens its air quality rules and the Balkans remain one of the continent’s pollution hotspots, this Belgrade campaign demonstrates how comprehensive chemical forensics can turn a hazy urban sky into a readable ledger of exactly what society burns, builds, drives and grows.

Subject of Research: Source apportionment and chemical characterization of PM10 particulate matter in Belgrade, Serbia

Article Title: Chemical characterization and source apportionment of PM10 in Belgrade, Serbia: influence of local and regional anthropogenic and natural sources

Article References: Petrović, B., Alastuey, A., Yttri, K. E., Pandolfi, M., Jovanović, M., Radović, B., Kovačević, R., Stojanović, D. B., Davidović, M., Platt, S. M., Bartonova, A., & Jovašević-Stojanović, M. (2026). Chemical characterization and source apportionment of PM 10 in Belgrade, Serbia: influence of local and regional anthropogenic and natural sources. Atmospheric Chemistry and Physics, 26(19), 14165-14184. https://doi.org/10.5194/acp-26-14165-2026

Image Credits: AI Generated

DOI: 10.5194/acp-26-14165-2026

Keywords: PM10, air pollution, source apportionment, biomass burning, Belgrade, positive matrix factorization, organic tracers, secondary organic aerosol, mineral dust, biogenic aerosols, heating season, Western Balkans