Characterization of PM2.5 chemical composition at the Demokritos suburban station, in Athens Greece. The influence of Saharan dust.

The aim of this work is to study the atmospheric concentrations of selected major and trace elements and ions found in PM2.5, at a suburban site in Athens, Greece, and discuss on the impact of the different sources. Special focus is given to the influence of Saharan dust episodes. The seasonal variability in the metal and ion concentrations is also examined. The results show that PM2.5 mass concentrations are significantly influenced by Saharan dust events; it is observed that when the PM2.5 concentration is higher than 25 μg/m3, five out of six times, the air mass crossed North Africa at an altitude within the boundary layer. Fe is found to be the element with the more significant seasonal variability, displaying much higher concentrations during cold period. The frequent Saharan dust intrusions in the cold period of this dataset may explain this result. Mineral dust and secondary aerosol are the main PM2.5 components (29 and 34%, respectively). During Saharan dust events, the concentration of mineral dust is increased by 35% compared to the days without dust intrusions, while an increase of 68% of the sea salt is also observed. During event days, PM2.5 concentrations are also increased by 14%. Anthropogenic components do not decrease during those days, while sulfate displays even a slight increase, suggesting enrichment of mineral dust with secondary sulfates. The results indicate that African dust intrusions add a rather significant PM pollution load even in the PM2.5 fraction, with implication to population exposure and human health.