Climatological analysis of aerosol optical properties over East Africa observed from space-borne sensors during 2001-2015

- Long-term spatiotemporal distributions of aerosol properties were studied over East Africa (EA).
- High values of aerosol parameters were observed during the local dry seasons in EA.
- South-north and west-east changes in AOD were noted during the dry period.
- Impact factor analyses showed significant effect on the AOD distribution in EA.

The present study is aimed at analyzing spatial and temporal characteristics of aerosols retrieved from MODerate resolution Imaging Spectroradiometer (MODIS) and Ozone Monitoring Instrument (OMI) sensors over East Africa (EA). Data spanning for a period of 15 years during 2001-2015 was used to investigate aerosol optical depth (AOD550), Ångstrom exponent (AE470-660) and absorption aerosol Index (AAI) over EA and selected locations within EA. Validation results of MODIS-Terra versus the Aerosol Robotic NETwork (AERONET) AOD550 revealed that the former underestimated aerosol loading over the studied regions due to uncertainties in surface reflectance. The annual mean AOD550, AAI, and AE470-660 were found to be 0.20 ± 0.01, 0.81 ± 0.03, and 1.39 ± 0.01, respectively with peak values observed during the local dry seasons. The spatial seasonal distributions of mean AOD550 suggested high (low) values during the local dry (wet) periods. The high AOD values found along the borders of southwest of Uganda were attributed to smoke particles; while higher (lower) values of AE470-660 (AAI) dominated most parts of the study domain. Low AOD (0.1-0.2) centers were located in high-altitude regions with relatively high vegetation cover over western and central parts of Kenya, and central and northern parts of Tanzania. Furthermore, latitudinal and longitudinal gradients in AOD550 showed a “southern low and northern high” and a “western low and eastern high” profile, respectively during JJA, as other seasons showed heterogeneous variations. Trend analysis revealed a general increase in AOD and AAI and a decrease in AE; while impact factors significantly affected AOD distribution over EA. HYSPLIT back trajectory analyses revealed diverse transport pathways originated from the Arabian Deserts, central Africa, and southwest of Indian Ocean along with locally produced aerosols during different seasons.

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