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

Fine particulate matter (PM_2.5) 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 PM_2.5 mass were sea salts modified by the presence of secondary sulfate-rich aerosols indicated also by principal component analysis. SO₄^2- was the prevailing anion, while the anthropogenic SO₄^2- (anth-nssSO₄^2-) dominantly constituted the major non-sea-salt SO₄^2- (nssSO₄^2-) fraction. Being influenced by the marine origin, its biogenic fraction (bio-nssSO₄^2-) 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 nssSO₄^2- 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 PM_2.5 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 PM_2.5 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.

Particle nucleation in the tropical boundary layer and its coupling to marine sulfur sources

New particle formation in a tropical marine boundary layer setting was characterized during NASA's Pacific Exploratory Mission-Tropics A program. It represents the clearest demonstration to date of aerosol nucleation and growth being linked to the natural marine sulfur cycle. This conclusion was based on real-time observations of dimethylsulfide, sulfur dioxide, sulfuric acid (gas), hydroxide, ozone, temperature, relative humidity, aerosol size and number distribution, and total aerosol surface area. Classic binary nucleation theory predicts no nucleation under the observed marine boundary layer conditions.