Long-term spatial and temporal variations of aerosol optical depth during 2000–2020 over Zambia, southcentral Africa

The study aimed at using Moderate Resolution Imaging Spectroradiometer (MODIS-Terra) to investigate long-term spatial and temporal aerosol variations over Zambia during 2000–2020. Based on data availability, ground truthing for MODIS-Terra was done over Mongu in western Zambia using Aerosol Robotic Network (AERONET) data for 2001–2009. The correlation coefficient between MODIS-Terra and AERONET is 0.42 and statistically significant at 95% confidence level. The aerosol optical depth at 550nm (AOD550) and Angstrom exponent (AE470-870) annual mean spatial distribution indicates high and moderate to low patterns explaining distinct features of aerosol loadings from different areas over Zambia. Generally, the AOD550 and AE470-870 spatial gradient values increase from southern to northern Zambia explaining fine mode particles mainly produced by local intensive anthropogenic and urban/small and large-scale industrial emission activities in the cities. Seasonal climatology reveals that highest AOD550 is observed during SON, followed by JJA, DJF, with the lowest recorded during MAM. It is also observed from AE470-870 that fine particles are prominent during JJA and SON. The insignificant decreasing (increasing) trend of AOD550 is revealed over Mwinilunga, Misamfu, Mfuwe, Choma, and Kabwe (Mongu). Further results showed that fire hotspot density intensifies over central parts of Africa, including Zambia from June to November. Moreover, the 5-day air mass back trajectory analysis suggests that aerosol sources over Zambia are associated with short- and long-distance ranges from East Africa, Congo Basin, Madagascar, and Atlantic and Indian oceans with diverse transport pathways in different seasons. These findings may help enhance a better understanding of climatic effects and atmospheric aerosol sources in Zambia.