Long-term trace gas and black carbon measurements at the high-altitude station Mount Kenya: tropical atmospheric variability and the influence of African emissions

Abstract. Long-term observations of atmospheric composition are essential for understanding regional and global climate impacts. Although the Global Atmosphere Watch (GAW) programme provides a network of worldwide measurements, continuous atmospheric measurements across Africa remain scarce. This study presents multi-year in-situ measurements of trace gases and black carbon from the Mount Kenya GAW station (MKN) from 2020 to 2024, offering a unique dataset from equatorial Africa. Its location exposes MKN to contrasting air masses from both hemispheres, enabling detection of emissions and providing insights into tropical variability such as seasonal and diurnal cycles. We present carbon dioxide (CO₂), methane (CH₄), carbon monoxide (CO), ozone (O₃), and black carbon (BC) measurements and compare these data with Copernicus Atmospheric Monitoring Service (CAMS) model products. While CAMS data broadly agree with the measurements, they underestimate diurnal variability and fail to capture O₃ and BC dynamics during rainy seasons, underscoring the importance of ground-based data for validating model performance. To identify source regions and sectoral emission contributions, we combined the FLEXPART particle dispersion model with satellite fire data, wetland emissions, and anthropogenic inventories. CO and BC were mainly linked to household fuel use and industrial energy, with biomass burning contributing during dry seasons. Methane variability was driven by agriculture and seasonal wetlands, but large uncertainties remain in all emission estimates. Our findings confirm the value of MKN observations for evaluating atmospheric models and emission inventories, and highlight the urgent need to expand measurement infrastructure across Africa to improve understanding of atmospheric processes and climate impacts.