People living in West Africa's densely populated southern cities face the highest exposure to nitrogen dioxide (NO₂) pollution, with urbanisation, industrial activity and seasonal biomass burning emerging as major drivers of the health-threatening pollutant, according to a new KNUST study.
The research, published in Environmental Pollution, provides the first regional satellite-based assessment of population exposure to NO₂ across West Africa.
It reveals that exposure is concentrated in major metropolitan and industrial corridors, including cities such as Lagos, Accra, Abidjan and Dakar.
Researchers led by Dr. Prince Junior Asilevi from theDepartment of Meteorology and Climate Science, combined data from the TROPOspheric Monitoring Instrument (TROPOMI) satellite with gridded population data to assess how pollution levels intersect with population distribution across the region.
The study found that while NO₂ pollution occurs across much of West Africa, the greatest exposure risk is concentrated in areas where elevated pollution coincides with large populations. Exposure levels were substantially higher during the dry season when widespread biomass burning and atmospheric conditions promote the accumulation of pollutants.
NO₂ is a major air pollutant produced mainly through fossil fuel combustion from vehicles, industries, power generation and biomass burning. Exposure has been linked to respiratory and cardiovascular diseases, asthma exacerbation, reduced lung function and increased hospital admissions.
The researchers reported significant positive relationships between population-weighted exposure and both urban land area and industrial activity, suggesting that rapid urbanisation and economic growth are key contributors to regional air pollution exposure.
Population-weighted exposure showed strong correlations with urban area and industrial land use, highlighting the influence of expanding cities and industries on air quality.
The study noted that population density is heavily concentrated along the southern coastal belt of West Africa, where major centres of economic activity and transportation infrastructure are located. These areas consequently emerge as major pollution hotspots.
According to the researchers, limited ground-based air quality monitoring across West Africa has hindered efforts to understand the full extent of pollution exposure in the region. Many countries lack comprehensive monitoring networks, making satellite observations an important tool for environmental and public health assessments.
The authors said their findings provide important evidence for policymakers seeking to improve air quality management, environmental monitoring and public health planning in West Africa.
"The results show that exposure risk is strongly concentrated in the densely populated southern corridor of the region, particularly in countries with large urban centres and extensive economic activity," the researchers concluded.
They added that satellite-based monitoring offers a practical approach for assessing pollution exposure in regions where ground monitoring infrastructure remains limited, providing a scientific basis for future interventions aimed at reducing air pollution and protecting public health.
