Summertime surface PM<sub>1</sub> aerosol composition and size by source region at the Lampedusa island in the central Mediterranean Sea

Abstract

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.

Measurement report: Fourteen months of real-time characterisation of the submicronic aerosol and its atmospheric dynamics at the Marseille–Longchamp supersite

“…The PM 1 chemical composition is consistent with results from PM 2.5 filters in MRS-LCP reported over the August 2011 to July 2012 period (Bozzetti et al, 2017;Salameh et al, 2015). The results are also comparable to those found in other Mediterranean coastal cities, where a noticeable proportion of sulfate is generally observed (Mallet et al, 2019;Minguillón et al, 2015;Stavroulas et al, 2019), whereas most urban sites in northern/central Europe show higher nitrate contribution (Lianou et al, 2011;Petit et al, 2015;Young et al, 2015).…”

Atmospheric deposition of organic matter at a remote site in the central Mediterranean Sea: implications for the marine ecosystem

“…The most intense dust deposition events on Lampedusa generally display higher values in spring (March-June) and in autumn (Vincent et al, 2016;Bergametti et al, 1989;Loÿe-Pilot and Martin, 1996;Avila et al, 1997;Ternon et al, 2010). In this study, we show that although dust events can significantly contribute to the annual DOC fluxes, sea spray seems to be the dominant source of DOC in this area, which is in agreement with Mallet et al (2019). The role of secondary organic aerosols as a source of organic matter in the Mediterranean Sea is well documented (Arndt et al, 2017;Michoud et al, 2017;Rinaldi et al, 2017) and could be relevant on Lampedusa.…”

“…PM 10 is sampled on a daily basis on the island of Lampedusa (Becagli et al, 2013;Marconi et al, 2014;Calzolai et al, 2015) by using a low-volume dual-channel sequential sam-pler (HYDRA FAI Instruments) equipped with two PM 10 sampling heads operating at a constant flow of 2.3 m 3 h −1 in accord with the European rules for aerosol monitoring (UNI EN12341). Aerosol is collected in 47 mm diameter Teflon filters (Pall Gelman) with 2 µm nominal porosity but certified to have 99 % retention efficiency for 0.3 µm diameter particles.…”

“…The DOC deposition was classified on the basis of the corresponding non-sea-salt (nss) Ca concentration in PM 10 (following Marconi et al, 2014;Fig. 6).…”

Online Chemical Characterization and Sources of Submicron Aerosol in the Major Mediterranean Port City of Piraeus, Greece

“…Therefore, the combined HOA components also retained a large contribution to OA (29%) in summer, in spite of improved atmospheric dispersion and the enhanced photochemical processing of primary hydrocarbons. While contributions of HOA in the order of 30% are in the upper echelon of values reported at urban sites in Europe and North America [71,134], they are comparable with the enhanced HOA contribution of 37% reported at the Houston Ship Channel, under the joint impact of vehicular and shipping emissions [39].…”