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University of Crete (2008)

Physical properties of aerosol particles affecting climate in the eastern Mediterranean atmosphere

KALIVITIS NIKOLAOS

Titre : Physical properties of aerosol particles affecting climate in the eastern Mediterranean atmosphere

Φυσικές ιδιότητες αιωρούμενων σωματιδίων με κλιματικό ενδιαφέρον στην ατμόσφαιρα της ανατολικής Μεσογείου

Auteur : KALIVITIS NIKOLAOS Καλυβίτης, Νικόλαος Πέτρου

Etablissement de soutenance : University of Crete

Grade : Doctor of Philosophy (PhD) 2008

Résumé partiel
The climatic effect of atmospheric aerosol particles has not yet been fully clarified. The high spatial and temporal variability of aerosol concentrations makes the investigation of their physical and chemical properties in global scale crucial in order to estimate their total climatic effect. Mediterranean Basin aerosol is of special interest for global climate research since a variety of aerosol types can be found there, namely marine aerosols, anthropogenic aerosols and desert dust aerosols. The environmental research station of the University of Crete at Finokalia has been pointed out as an anchor station for the Eastern Mediterranean basin. The present work focuses on the physical properties of atmospheric aerosol particles at the station of Finokalia and three scientific goals have been distinguished : the study of aerosol particles size distributions in the area, the study of aerosol optical properties and the study of mineral dust events over the eastern Mediterranean. For the first time in the Eastern Mediterranean basin have the aerosol particle size distributions been measured on a regular basis and for a length of time long enough to investigate their temporal variations. Two separate periods of measurements took place, the first from July 2004 until January 2005 and the second from August until July 2005 and during both periods the same tendencies were revealed. The most important observation is the depletion of aerosol particles with smaller diameter than 50 nm. Two patterns of depletion have been observed. The first pattern is characterized by a gradual depletion of the particles. In general, this pattern is not necessarily related to diurnal variation of solar irradiance, as its initiation appeared in the late afternoon or even before sunrise. The second pattern occurred only during day time and the maximum depletion was observed at noon or in the early afternoon while the depletion rate was more rapid. Both the depletion intensity and the frequency of the depletion events, decreased from summer to winter. We compared these observations with simplistic box model simulations of the particle size distribution involving only condensation of sulfuric acid and coagulation on larger particles. Τhe agreement of observations and simulations for the second pattern of depletion suggests that condensation of sulfuric acid vapors and coagulation are the main factors controlling this phenomenon while for the first pattern the depletion of small particles must be attributed to some other semi-volatile species because of the low concentrations of sulfuric acid during nighttime.

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