10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Aerosol Optical Characteristics of Sub Saharan Area
Rajae Meziane, MOHAMMED DIOURI, Atmospheric Physic, LME, University of Oujda, Morocco
Abstract Number: 1323 Working Group: Remote/Regional Atmospheric Aerosol
Abstract The present study is devoted to the aerosol optical characterization including PSD, based on data of Aerosol Optical Depths determined with sun photometric measurements for five Sub-Saharan sites, Bujumbura (3.38S, 29.38E), Mongu(15.26S, 23.13E), Gabon(0.20S,11.60E), Namibia(15.15S, 12.17E) and Pretoria(25.75S, 28.28E) and the Atlantic St-Helena Island (15.94S,5.66W) as a reference site. Measurements are made of AERONET/PHOTONS network set up by the Goddard Space Flight Center (NASA, USA) and the Laboratory of Atmospheric Optics (CNRS, France). Sub-Saharan Africa is composed of several types of climate, the main one being that of the tropical savannah that bypasses the equatorial climate. In the South, the subtropical region at first quite humid then tempered until desert.
The seasonal averages of aerosol optical depth at 0.5µm show two categories with low level less of 0.4 near the southern coast as in Mongo, Durban and Pretoria and high level reaching 1.2 for continental sites as Bujumbura and Gabon. Values for St-Helena do not exceed 0.1 outside disturbances observed on August and September. Seasonal averages of single scattering albedo at all wavelengths varies on a large interval (0.4 to 0.98) for continental sites and on a reduced interval (0.8 to 0.95) for the other sites. The radiative forcing observed at the top of the atmosphere varies between -50 and -120W/m2, expressing the increase of the reflected flux contributing to cooling of the Earth-Atmosphere. At the surface, the observed values vary between -200 and -150W/m2, that quantify the local cooling tendency. This tendency is more accentuated reaching -450 W/m2 in Mongu consistent with the large variability of the observed single scattering albedo, and the high surface albedo.
The monthly means of PSD show very higher amplitudes for both coarse and fine modes respectively around an average radius of 5µm and 0.15µm with a maximum recorded in spring for Gabon and Bujumbura expressing an important natural and anthropogenic local pollution. For the other sites, we observe very lower amplitudes around 0.1 and 4 µm respectively for coarse and fine modes that indicate healthy air consistent with the registered AOD values.