Chemical characterization of fine aerosols in respect to water-soluble ions at the eastern Middle Adriatic coast

Fine particulate matter (PM₂.₅) concentrations at the Middle Adriatic coastal site of Croatia were affected by different air-mass inflows and/or local sources and meteorological conditions, and peaked in summer. More polluted continental air-mass inflows mostly affected the area in the winter period, while southern marine pathways had higher impact in spring and summer. Chemical characterization of the water-soluble inorganic and organic ionic constituents is discussed with respect to seasonal trends, possible sources, and air-mass inputs. The largest contributors to the PM₂.₅ mass were sea salts modified by the presence of secondary sulfate-rich aerosols indicated also by principal component analysis. SO₄²⁻ was the prevailing anion, while the anthropogenic SO₄²⁻ (anth-nssSO₄²⁻) dominantly constituted the major non-sea-salt SO₄²⁻ (nssSO₄²⁻) fraction. Being influenced by the marine origin, its biogenic fraction (bio-nssSO₄²⁻) increased particularly in the spring. During the investigated period, aerosols were generally acidic. High Cl⁻ deficit was observed at Middle Adriatic location for which the acid displacement is primarily responsible. With nssSO₄²⁻ being dominant in Cl⁻ depletion, sulfur-containing species from anthropogenic pollution emissions may have profound impact on atmospheric composition through altering chlorine chemistry in this region. However, when accounting for the neutralization of H₂SO₄ by NH₃, the potential of HNO₃ and organic acids to considerably influence Cl⁻ depletion is shown to increase. Intensive open-fire events substantially increased the PM₂.₅ concentrations and changed the water-soluble ion composition and aerosol acidity in summer of 2015. To our knowledge, this work presents the first time-resolved data evaluating the seasonal composition of water-soluble ions and their possible sources in PM₂.₅ at the Middle Adriatic area. This study contributes towards a better understanding of atmospheric composition in the coastal Adriatic area and serves as a basis for the comparison with future studies related to the air quality at the coastal Adriatic and/or Mediterranean regions.