Major systematic contribution of fine aerosols over southern Africa from rivers of smoke depicted from spaceborne multiyear observations

Southern Africa is a climate-vulnerable region affected by biomass burning aerosols (BBA) emitted seasonally in central Africa, the primary source globally. By absorbing radiation and by deposition, these BBA have the potential of affecting in a very significant way both the regional radiative budget, the local meteorology and biogeochemistry, henceforth the regional climate. These impacts are governed by the high variability inherent to the fires and the short-lived atmospheric species.In this study, we use satellite measurement of total column CO from three IASI instruments and the aerosol optical depth (AOD) by MODIS from 2007 to 2023, to investigate the climatology of transported BBA across the subcontinent at a daily timescale. We identify the seasonality, pathways and contribution of a meteorological phenomenon of the “rivers of smoke”, where the BBA plume is embedded in synoptic system, transporting high concentration of aerosol in the mid latitudes.This intermittent transport happens seasonally, primarily above the continent, with a frequent second pathway along the western coast. The African regime, characterized by systematic fire and intermittent mid-latitude transport, contrasts with other important sources of tropical fire in the Amazon and southeast Asia. Our analysis reveals a maximum of contribution to the CO by the river of smoke in the southern Indian Ocean at 40°S. This pathway accounts for 25 to 30% of the regional CO concentration and peaks in September. In addition, the BBA, which are known to be in the fine mode, form plumes that contributes up to 60% of the fine mode fraction of AOD retrieved from MODIS in Namibia and South Africa, while the peak of contribution is in August, closer to the peak fire activity in July.The river of smoke database from satellite observations established in this work provides a robust framework to tackle the variability of BBA.