Raman Lidar Monitoring of Extinction and Backscattering of African Dust Layers and Dust Characterization

Results on the monitoring of strong African dust outbreaks at Lecce in the southeastern corner of Italy (40 °20 ‘ N, 18 °6 ‘ E) during May 2001 are presented. This activity has been performed in the framework of the European Aerosol Research Lidar Network (EARLINET). The lidar station of Lecce is located on a flat rural area that is approximately 800 km from the northern Africa coast. So it is closer to Africa than most of all other EARLINET stations and allow monitoring African dust transport early in its life cycle, at all levels in the plume. An elastic-backscatter Raman lidar based on a XeF excimer laser (351 nm) has been used to monitor the time evolution and vertical structure of the dust layers and get independent measurements of the aerosol extinction and backscatter coefficients. The findings are presented in terms of vertical profiles of the extinction and backscatter coefficients and of the lidar ratio. A quite deep dust layer extending between 2 and 6 km and characterized by a backscatter coefficient of ~0.0016 (km sr)-1 , a lidar ratio of approximately 50 sr, and an aerosol optical depth of 0.26 was observed on 17 May 2001 between 18:55 and 20:07 UT. The layer persisted for approximately five days. Dust layers of lower optical thickness and shorter persistence time have generally been monitored at the lidar site during African dust outbreaks. Results on the chemical and morphological characterization of the dust collected at the lidar station are also given to further support the origin of the monitored aerosol layers.