Spatial and temporal variability of aerosol:: size distribution and optical properties

Spectral optical thickness measurements together with sky radiance measurements at Ouagad gou (Burkina-Faso), Banizoumbou (Niger), Thala (Tunisia), IMC Oristano (Sardinia) and Rome Vergata (Italy) during April, May and June 2001 have been used to derive aerosol characteristics spatial and temporal variations of aerosol optical thickness tau(a), aerosol size distribution and sin! scattering albedo. The analysed tau(a) data at the different sites show a high spatial variability of aerosol optical thickness. The tau(a) values at 870 nm obtained during the study period show that 97% the data vary between 0.1 and 1.5 for central African sites (Ouagadougou and Banizoumbou) between 0.03 and 1 for Mediterranean sites (IMC Oristano, Rome Tor Vergata and Thala). The Angstrom wavelength exponent a was found to vary with the magnitude of the aerosol optical thickness. The higher and lower values of a correspond to the lower and higher values of respectively. In European sites, alpha varies between 0.2 and greater than 2.0. In Thala, it ranges from to 1.8 and for central Aftican stations, a exhibited variability from (-0.1) to approximately 0. The size distribution inversion obtained by combining the spectral optical thickness from di sun measurement and aureole data presents three radius modes in both Mediterranean sites central African sites: the first mode with radius near 0. 1 mum and two second modes with radius at 4 gm. The effective and volume weighted radii are computed for the five studied sites and company. The single-scattering albedo omega(o), obtained from solar aureole data at African sites, shows an increase of omega(o), with wavelength for different aerosol optical thickness values. (C) 2002 Elsevier Science B.V All rights reserved.