Chemical Speciation and Source Apportionment of PM_2.5 in Greek Urban and Suburban Areas: Insights from the PANACEA Initiative

Abstract. This study, conducted under the PANhellenic infrastructure for Atmospheric Composition and climatE chAnge (PANACEA), examines PM₂.₅ chemical speciation and source apportionment across five Greek cities (Athens, Ioannina, Patras, Volos, and Xanthi) representing urban background, urban, and rural environments. Sampling was conducted during summer (June to August 2019) and winter (December 2019 to February 2020), complemented by an earlier campaign at Athens Thissio (December 2018 to August 2019), yielding over 545 24-hour PM₂.₅ samples. Filters were analyzed for major and trace elements, water-soluble ions, organic carbon (OC), and elemental carbon (EC). Positive Matrix Factorization (PMF) was applied separately for each site using a harmonized protocol. Seven source categories were identified across the network: biomass burning (16.2 % to 50.9 %), heavy oil combustion (2.5 % to 15.1 %), industrial emissions (3.3 % to 14.4 %), mineral dust (4.8 % to 16.4 %), sea salt (1.6 % to 11.7 %), secondary sulfates and organics (7.1 % to 33.0 %), and vehicular traffic (9.7 % to 27.6 %). Campaign-average PM₂.₅ concentrations in Ioannina and Volos remained above 25 μg m⁻³, pointing to severe air pollution burdens and a high risk of non-compliance with European standards. The high spatial and temporal variation in source contributions reveals that while regional background pollution strongly influences PM₂.₅ levels, localized anthropogenic activities, and particularly wintertime biomass burning for residential heating, remain a critical driver of urban air quality degradation in Greece.