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Home  >  Volume 21 (2012)

Radiative Forcing of Urban Aerosols in the Visible Region by B. I. Tijjani Volume 21 (July, 2012), pp 151 – 162
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The optical and microphysical properties of urban aerosols at the visible region (0.40μm to 0.75μm) at relative humidities (RHs) 0, 50, 70, 80, 90, 95, 98 and 99% are extracted from the Optical Properties of Aerosol and Clouds software. The optical parameters extracted are refractive indices, radii of water soluble components, scattering, absorption, and extinction coefficients, single scattering albedos, asymmetry paramenters and τsca and τaba as the aerosol layer scattering and absorption optical thickness. The data was used to calculate the radiative forcings(RF), Angstom parameters, hygroscopic growth factors, and hgroscopicities. Angstrom parameters that are used to determine the nature of the particles size distributions at different RHs are obtained using the aerosols optical depths. Angstrom parameters increase from 1.0842 at 0% RH to 1.1677 at 80% RH as a result of hygroscopic growth and decrease from 1.1677 at 80%  RH to 0.9722 at 99% as a result of coagulation due to the increase in RH. It also shows that increase in RH has caused increase in mode size distributions which caused increase in radiative cooling. The analysis further shows that these aerosols have Junge type of size distributions and are dominated by fine mode particles distribution which account for the observed negative RF.