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Abstract
In this study we present geometrical properties of aerosol particle pollution in the free troposphere over Thessaloniki, Greece. We have used routinely measurements that have been performed using a backscatter/Raman lidar from January 2001 to December 2007 in the framework of the European Aerosol Research Lidar Network (EARLINET). In summary, we analuze 343 measurements, from which 152 are performed during night and the rest 191 are daily mesurements. Specifically, in this work we present statistical information on geometrical properties of free-tropospheric particle layers and its dependence on different air mass sources. In order to do that, we determine the geometrical depth of the particle layers by the use of range corrected backscatter signals at 355 nm for night measurements and 532 for daily measurements. We statistically analyze our measurements by frequency distribution on the basis of all measurements and find out that most pollution events occur in late spring and throughout the summer months. We have also calculated the frequency distribution of bottom, top, center and depth of the free-tropospheric layers. Finally, we use backward trajectory analysis with Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) to identify the main sourse regions of the free-tropospheric particles. A pollution event may be characterized with one, two, or more pollution layers from different source regions. For that reason we attribute pollution events to different source regions, if backward trajectories indicate multiple source regions. In the future we shall analyze our 7-year data set for each geometrical layer identified with respect to optical and microphysical particle properies.