| Abstract |
Fine marine aerosols influence the climate system by acting as cloud condensation nuclei (CCN) in the atmosphere. The organic chemical composition and origin of the marine fine particulate matter are still largely unknown, because of the insufficient reports on in situ studies, the large variability in the emission from the sea, from the complex transfer of gases and particles at the air-sea interface, and the transport of aerosol particles from very distant sources. As important processes of formation of marine organic aerosol production are considered: transport of terrestrial particles, secondary organic aerosol (SOA) formation from the oxidation of biogenic dimethyl-sulfide (DMS), and biogenic particle emissions through sea spray. Specific compounds related to the above-mentioned processes have been proposed as molecular markers: e.g. n-alkanoic acids and n-alkanes (terrestrial particles), levoglucosan (biomass burning aerosol), aminoacids (biological terrestrial or marine particles), methanesulphonate (MSA) (DMS oxidation), C8 and C9 dicarboxylic acids and oxo-carboxylic acids (marine SOA) and other short-chain dicarboxylic acids (marine or terrestrial SOA), and humic-like compounds (emission of marine organic carbon). In this study, an effort was made to characterize the water-soluble organic fraction of marine aerosols collected at a background sampling site of Eastern Mediterranean at Finokalia of Crete. The sampling period was 2007-2008. In order to identify and quantify the water-soluble organic compounds of marine aerosols determined in the present study gas chromatography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), nuclear magnetic resonance spectroscopy (NMR) and ion chromatography (IC) were used. The origin of air masses arriving in the study area was studied by using backward trajectories calculation (NOAA HYSPLIT Model). In addition the “MODIS fire products” for fire detects was used. Measurements of collective parameters such as organic/elemental carbon (OC/EC), dissolved organic carbon (DOC), and aerosol surface active substances as methylene blue active substances (MBAS) were also performed. The concentration ranges for total suspended particles (TSP) was 12.3-61.1 μg m-3, for OC and EC 0.6-2.2 μg m-3 and 0.1-0.4 μg m-3 respectively, for DOC 0.7-1.8 μg m-3, and for MBAS 7.4-15.4 ng m-3. The average ratio OC/EC was 6.9 (±3.5) and the proportion of DCO in relation to OC was 83 (±13) %, indicating a high degree of oxidation in the water-soluble organic matter. OC and DOC were statistically strongly correlated with the intensity of fire events in southern Europe.
The analysis of the water soluble organic extract by GC/MS, NMR and IC revealed the presence of 109 individual organic compounds which made the 12-29% % of DOC. The most significant categories were: I) Twenty six n-alkanoic acids were detected with an average concentration of 145 ng m-3. Formic acid, acetic acid, tridecanoic and heneicosanoic acids demonstrated the highest correlation with fire events. II) Twenty two saturated, unsaturated and branched dicarboxylic acids were analysed with an average concentration of 526 ng m-3. The highest statistical correlation with fire events was determined for the concentration of dicarboxylic acids with Cn >6. III) Thirty one (31) hydroxy-, oxo- and keto- carboxylic and dicarboxylic acids were also determined. Their average concentration was 126 ng m-3. The most significant statistical correlation with fire events were determined for the concentration of glycolic acid and 7keto-octanoic acid. IV) Various aromatic acids and polycarboxylic acids, such as 4-hydroxy-benzoic acid, vanillic acid, syringic acid and trans-7-carbomethoxy-2-octendioic acid have shown the highest correlation with fire events. V) Pinic and pinonic acids were present in relatively low concentrations (ca. 3 ng m-3). It is interesting that organosulfates of these acids were determined in the Eastern Mediterranean marine aerosol by using LC/MS. The results of this study show that fire events (biomass burning) in southern Europe is a major source of water-soluble oxygenated organic compounds in the marine atmosphere. The concurrent use of mass spectrometry and NMR techniques allowed a better determination of the organic content of marine aerosols.
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Μελέτη του οργανικού κλάσματος των πρωτογενών και δευτερογνών αιωρούμενων σωματιδίων της ανατολικής Μεσογείου
