Seasonal patterns of Saharan Dust detected over the central Mediterranean basin, at the High-altitude Monte Curcio GAW Station

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Seasonal patterns of Saharan Dust detected over the central Mediterranean basin, at the High-altitude Monte Curcio GAW Station

Mariantonia Bencardino, Andreoli Virginia, Jessica Castagna, Francesco D’Amore, Valentino Mannarino, Sacha Moretti, Attilio Naccarato, Antonella Tassone, Francesca Sprovieri, Nicola Pirrone

The High-altitude Monte Curcio station is part of the Global Mercury Observations System (GMOS) as well as of the Global Atmosphere Watching (GAW) networks has been used since 2015 to gather high-temporal resolution, quality controlled data on atmospheric mercury, greenhouse gases and the physical-chemical properties of aerosols. The station is not influenced by local anthropogenic sources being instead able to intercept long-range transported air masses. These last may include industrial pollutants from continental Europe, sea spray from the surrounding Mediterranean Sea, volcanic ashes from the nearby Etna and Stromboli volcanoes as well as mineral dust from the Saharan desert. Among various atmospheric monitoring pollutants, 24-h PM10 and PM2.5 samples were simultaneously collected. In total, about 300 samples have been gained, for both the finer and coarser size fractions of PM, and then analyzed by the thermo-optical method to quantify their Organic and Elemental Carbon concentrations (OC and EC). Starting from April 2016 until June 2017, an extensive and quite continuous data series on PM levels and its carbonaceous content was thus obtained for the first time at the southernmost part of Italy as representative for the regional area of the central Mediterranean basin. Mean background levels of PM2.5 and PM10 were 5.6 ± 3.0 and 9.0 ± 6.0 μgm-3, respectively, while the same reached the averaged levels of 13.7 ± 8.4 and 43.3 ± 32.4 μg m-3 in conjunction with dust outbreaks. A clear seasonal pattern was identified with spring characterized by a major influence of Saharan intrusions both in terms of frequency and intensity, while no such events observed in winter. Synoptic and local wind fields were analyzed and discussed in terms of the observed PM seasonal variability. The availability of the carbon content provided insights about the possible association of OC to mineral dust contrarily to the EC component that was instead more influenced by wildfire events, that occurred a lot in summer and locally around our monitoring area. The comparison of carbon species and their share between the fine and coarse PM fractions resulted useful in discriminating the prevailing sources at our monitoring station.

Keywords: High-altitude station, Saharan Dust, Wildfires, Elemental Carbon

Proscience vol. 5

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