Summertime surface PM1 aerosol composition and size by source region at the Lampedusa island in the central Mediterranean Sea
Authors: Mallet Marc D. , D'Anna Barbara , Même Aurélie , Bove Maria Chiara , Cassola Federico , Pace Giandomenico , Desboeufs Karine , Di Biagio Claudia , Doussin Jean-Francois , Maille Michel , Massabò Dario , Sciare Jean , Zapf Pascal , di Sarra Alcide Giorgio , Formenti Paola 
Published: September 2019

Abstract. Measurements of aerosol composition and size distributions were taken during
the summer of 2013 at the remote island of Lampedusa in the southern central
Mediterranean Sea. These measurements were part of the ChArMEx/ADRIMED
(Chemistry and Aerosol Mediterranean Experiment/Aerosol Direct Radiative
Forcing on the Mediterranean Climate) framework and took place during
Special Observation Period 1a (SOP-1a) from 11 June to 5 July 2013. From compact time-of-flight aerosol mass spectrometer (cToF-AMS)
measurements in the size range below 1 µm in aerodynamic diameter
(PM1), particles were predominately comprised of ammonium and sulfate. On
average, ammonium sulfate contributed 63 % to the non-refractory PM1
mass, followed by organics (33 %). The organic aerosol was generally very
highly oxidized (f44 values were typically between 0.25 and 0.26). The
contribution of ammonium sulfate was generally higher than organic aerosol
in comparison to measurements taken in the western Mediterranean but is
consistent with studies undertaken in the eastern basin. Source apportionment of organics using a statistical (positive matrix
factorization) model revealed four factors: a hydrocarbon-like organic
aerosol (HOA), a methanesulfonic-acid-related oxygenated organic aerosol
(MSA-OOA), a more oxidized oxygenated organic aerosol (MO-OOA) and a less
oxidized oxygenated organic aerosol (LO-OOA). The MO-OOA was the
dominant factor for most of the campaign (53 % of the PM1 OA mass). It was
well correlated with SO42-, highly oxidized and generally more
dominant during easterly air masses originating from the eastern
Mediterranean and central Europe. The LO-OOA factor had a very similar
composition to the MO-OOA factor but was more prevalent during westerly
winds, with air masses originating from the Atlantic Ocean, the western
Mediterranean and at high altitudes over France and Spain from mistral
winds. The MSA-OOA factor contributed an average 12 % to the PM1 OA and
was more dominant during the mistral winds. The HOA, representing observed
primary organic aerosol, only contributed 8 % of the average PM1 OA during
the campaign. Even though Lampedusa is one of the most remote sites in the Mediterranean,
PM1 concentrations (10 ± 5 µg m−3) were comparable to those
observed in coastal cities and sites closer to continental Europe. Cleaner
conditions corresponded to higher wind speeds. Nucleation and growth of new
aerosol particles was observed during periods of north-westerly winds. From a
climatology analysis from 1999 to 2012, these periods were much more
prevalent during the measurement campaign than during the preceding 13 years.
These results support previous findings that highlight the importance
of different large-scale synoptic conditions in determining the regional and
local aerosol composition and oxidation and also suggest that a non-polluted
surface atmosphere over the Mediterranean is rare.