TITLE:
Long-Term Merra-2 Characterization of Black Carbon’s Surface Mass Concentrations and Its Impact to Climate Change over East Africa
AUTHORS:
Jacob W. Kutoto, John W. Makokha, Tom Ekisa, Geoffrey W. Khamala
KEYWORDS:
Black Carbon, MERRA-2, East Africa
JOURNAL NAME:
Atmospheric and Climate Sciences,
Vol.15 No.4,
September
30,
2025
ABSTRACT: Black carbon (BC), which is one of the short-lived climate forcers, largely influences the local modulation of the climate, particularly in regions that are sensitive such as East Africa. However, the long-term trends and meteorological impacts of BC in this region remain not very well investigated, especially considering the context of altered anthropogenic and natural emission sources. This study bridges this gap through a comprehensive spatio-temporal examination of BC surface mass concentration for East Africa from 1980 to 2023 using data from the Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2). It has also established statistical correlation between BC concentrations and the selected meteorological parameters, i.e., surface air temperature, specific humidity, surface wind speed, and total surface precipitation. Time-series analysis, spatial visualization, and Pearson correlation were applied to analyze the MERRA-2 datasets. Results showed pronounced intra- and inter-annual variability in BC distribution with high concentrations (>8 × 10−12 kg/m3) mostly over western Uganda and northwestern Kenya and Tanzania during boreal winter. Such space hotspots were linked to both local sources (biomass burning, automobile pollution) and long-range atmospheric transport from Asian and Middle Eastern industrial regions. The effect of natural sources such as West African bushfires and Saharan dust storms, was also reflected by transboundary dispersion patterns due to wind systems in operation. Correlation analysis found that surface wind speed showed a statistically significant negative correlation with BC concentrations during all seasons, particularly March-May (r = −0.57, R2 = 0.31) and June-August (r = −0.51, R2 = 0.24), indicating high winds favour BC dispersion. Specific humidity in addition to precipitation was moderately positively correlated with BC, particularly during the September-November season (r = 0.47, R2 = 0.20), showing complex interactions between atmospheric moisture and aerosol lifecycles. Surface air temperature was most strongly seasonally correlated with BC during the short rains (r = 0.55, R2 = 0.29), showing the two-way effect of BC on atmospheric warming and radiative forcing. In short, the investigation indicates that BC concentrations over East Africa exhibit distinct spatial and temporal patterns driven by both human and natural processes. The statistically significant correlations with meteorological parameters prove the modulating role of BC in regional climate processes. Policymakers must prioritize emission control actions targeted at biomass burning and urban pollution, and scientists must keep investigating high-resolution BC-climate interactions using integrated ground and satellite observations to advance climate impact assessment in East Africa.