Estimation of Radiative Forcing due to Aerosols over Selected Sites in Kenya

Abstract

Atmospheric aerosols modulate the radiative budget and ambient air quality of the atmosphere, thus, there is a need to develop both analytical and computational methodological techniques that determine their physical, chemical, optical and radiative properties in order to characterize and model their environmental effects. This paper embodies the results of the derivation of radiative characteristics of the atmosphere over Nairobi, Mbita and Malindi using aerosol data obtained from sun spectrophotometry from 2006-2008. Aerosol optical depths (τ), single scattering albedo (ω), angstrom exponent (α), asymmetry factor (g) at zero Solar Zenith Angle (SZA) were derived through AErosol RObotic NETwork (AERONET) framework. The Coupled Ocean and Atmosphere Radiative Transfer (COART) model was then used to solve a radiative transfer equation (RTE) for an atmosphere modulated by aerosols of different particle sizes. Utilizing the integrated fluxes, radiative forcing due to atmospheric aerosols was estimated, and found to remain relatively constant at 0.46 K/(W/m2) for all the three sites despite the observed differences in the various aerosol particle properties that is physical, mode of generation, chemical and number densities dominating the sites. This value was slightly lower as compared to the combined global anthropogenic radiative forcing estimated to be +1.6 [-1.0, +0.8] W/m2.