| Abstract |
The present work is focused on the study of the organic fraction of aerosols in the Eastern Mediterranean atmosphere and its role in the formation of cloud condensa-tion nuclei. For the size-resolved distribution of the organic and elemental carbon a 12-stage impactor was used, whereas CCN measurements were performed by a DMT-CCN counter, with concurrent monitoring of the particle distribution of the aerosols. The dis-tribution measurements of organic and elemental carbon took place at a natural marine site from July 2004 to February 2007 and the CCN measurements from July to October 2007 and from June to July 2008.
Both organic and elemental carbon depict a distinct seasonal variability charac-terized by summer maximum and winter minimum concentrations. The largest part of the total mass of the organic and elemental carbon is assigned to particles in the ac-cumulation mode, coming from combustion (fossil fuel but also biomass burning), ar-riving at the area from Central and Northeastern Europe and countries surrounding the Black Sea. The contribution of the coarse fraction to the total concentrations is of 25% whilst from further investigation, 64±14% of the fine organic fraction was found to be water-soluble. Hence it can be concluded that the organic aerosols that arrive in the area are mainly secondary, highly oxidized and water-soluble, and of low volatility.
From the cloud condensation nuclei measurements it was shown that air masses originating from less polluted areas, tend to have lower particle concentrations, with larger CCN and seem to be more activated. Practically all particles are activated in high supersaturations (0.8%), which is expected due to the degree of oxidation of the aerosols. From the size-resolved measurements of the CCN it can be seen that the par-ticles are an internal mixture during most of the day, with great homogeneity. It is only around noon that a change in the chemical composition appears, manifested by a drop in the activation fraction, especially at low supersaturations. With the use of “simple” Köhler theory, size-distribution and bulk chemical composition measurements, a very satisfactory closure, of predicted and measured values, is attained. Taking into consid-eration the water-soluble organic carbon, the error and the scatter of the results are reduced considerably. Finally, from the droplet growth kinetics it was revealed that the presence of organics does not seem to repress the growth rate of particles, by water uptake.
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Οργανικός άνθρακας στην ατμόσφαιρα της Α. Μεσογείου και ο ρόλος του στον σχηματισμό πυρήνων συμπύκνωσης νεφών (CCN)
