Optical properties of Saharan dust layers as detected by a Raman lidar at Thessaloniki, Greece

Measurements during Saharan dust transport events were performed at several stations of the European Aerosol Research Lidar Network. During the period 2001 - 2002, 12 cases were captured at Thessaloniki, Greece ( 40.5 degrees N, 22.9 degrees E) with a 355 nm Raman lidar. For these cases the vertical profiles of the extinction and backscatter coefficients were determined and examined, as well as profiles of extinction-to-backscatter ratio ( lidar ratio) and the backscatter-related Angstrom exponent between 355 and 532 nm ( color index). Model calculations from the DREAM model confirmed the existence of Saharan dust in all cases examined. Within the dust plumes the lidar ratios ranged from 20 to 100 sr and the color index ranged from - 1 to 3. An anticorrelation was found between the lidar ratio and the color index during the Saharan dust events. In certain cases the results suggest that the mixing of dust particles with boundary layer aerosols reduces the dust 'signature' and thus, makes difficult the separation of the dust particles from those of mostly urban origin.