Spatial-Temporal Variation of Aerosol Optical Depth and Ångström Exponent over Selected Towns in Kenya: Environmental Impact and Climate Change

Abstract

Aerosol optical depth (AOD) and Ångström Exponent (AE) have become the most crucial metrics in assessing climate change. Despite this, studies related to AOD and AE are rare in Kenya. Using Moderate Resolution Imaging Spectroradiometer (MODIS) data, the present study analysed the spatial and temporal variations of aerosol optical depth at 550 nm (AOD550) and examined the impact of these variations on AE over eight selected towns in Kenya during 2001-2021. The findings indicated high (0.22 ± 0.04) AOD during June-July-August-September (JJAS) and low (0.12 ± 0.04) values during March-April-May (MAM), all associated with prevailing local meteorological conditions. The Ångström Exponent in the wavelength (412 μm - 470 μm) was found to be high (1.1 - 1.7) in most towns, attributed to the dominance of fine-mode particles from increased anthropogenic activities. However, AE412-470 exhibited relatively low values in the range of 0.7 to 1.0 in Garissa due to the dominance of coarse mode particles associated with increased dust particles. Also, the coastal regions of Kenya have moderate to high values of AE412-470 associated with industrial emissions from the urbanized coastal regions of Mombasa. The study has contributed to an in-depth understanding of spatial-temporal variations of AOD and AE over the selected towns in Kenya and forms a scientific basis for further research on aerosol science over the region.