Urban aerosol organics in the Eastern Mediterranean: source apportionment and molecular insights

Urban atmospheric particulate matter (PM) pollution poses significant environmental and health problems. The knowledge of the pollution sources and their contribution to air quality can lead to more effective future mitigation strategies for reducing air pollution. We report continuous Aerosol Chemical Speciation Monitor (ACSM) measurements at a traffic urban station in Heraklion (Crete, Eastern Mediterranean) during 2024. To quantify organic aerosol (OA) sources and their temporal dynamics, a positive matrix factorization (PMF) analysis was performed. This analysis was supported by co-located black carbon measurements and trace gas measurements. The resolved factors indicate i) traffic-related OA (HOA) with pronounced diurnal variability consistent with traffic activity, ii) cooking-related OA, iii) biomass burning OA alongside iv) oxygenated OA components linked to secondary aerosol formation and long-range transport. The ACSM-based PMF information was complemented by offline aerosol chemical characterization. About hundred 24h PM10​ filters were collected and analyzed to characterize the organic fraction using untargeted liquid chromatography high resolution mass spectrometry (Orbitrap). This offline dataset provides molecular-level information (elemental classes and marker compounds) enabling deeper understanding of the molecular profile of each pollution source and provides aerosol processing details. Financial support from Region of Crete through the project “Action Plan for Addressing Air Pollution in the Region of Crete” is greatly acknowledged. We acknowledge support by Horizon Europe project Net4Cities Contract No. 101138405