Population exposure to nitrogen dioxide (NO2) pollution in West Africa.

Nitrogen dioxide (NO2) is a major atmospheric pollutant associated with combustion emissions and adverse human health outcomes. In West Africa, however, limited ground-based monitoring has hindered regional assessment of population exposure to air pollution. This work leverages the TROPOspheric Monitoring Instrument (TROPOMI) and gridded population density data to develop and evaluate the population exposure pattern to NO2 across West Africa. A population-weighted exposure (PWE) metric was developed to quantify exposure intensity in inhabited areas (≥50 people km-2). Spatial patterns of NO2 were examined alongside fire activity, urban extent, industrial area, and transport infrastructure to identify potential drivers of exposure. Results show that NO2 levels and population exposure are strongly concentrated in the densely populated southern belt of West Africa, particularly along major urban and industrial corridors. Exposure levels are substantially higher during the dry season when widespread biomass burning and atmospheric conditions enhance pollutant accumulation. Across countries, PWE shows significant positive relationships with both urban area (r ≈ 0.77) and industrial land use (r ≈ 0.68), highlighting the influence of urbanisation and economic activity on regional air pollution exposure. These findings provide the first regional satellite-based assessment of NO2 exposure risk in West Africa and offer important insights for air-quality management and public health planning.