Air pollution levels in several Sub-Saharan African cities and power plants are significantly different from what widely used global databases report, a new study says.
For the study published in JGR Atmospheres, researchers used data from the European satellite instrument Tropospheric Monitoring Instrument (TROPOMI) to measure nitrogen oxide (NOx) emissions from 24 major pollution hotspots across the region—including 21 cities and three coal-fired power plants.
Nitrogen oxides are harmful gases produced mainly by vehicles, generators, industrial activity and power plants. They contribute to smog, respiratory illness and climate change.
The study found that the 24 hotspots together emit about 312,000 tonnes of nitrogen oxides per year.
Urban emissions ranged from very low levels in smaller cities to much higher levels in large metropolitan areas. Lagos, Nigeria, recorded the highest urban emissions in the study. Meanwhile, coal-fired power plants in South Africa were among the largest single sources of pollution measured.
The researchers said Sub-Saharan Africa is becoming a major global source of air pollution but reliable local emissions data remain scarce.
“Sub-Saharan Africa is an increasingly dominant global source of air pollution,” the study states, noting that many countries in the region lack the resources to build consistent, high-quality pollution inventories.
To address this gap, the team analyzed satellite images of pollution plumes–clouds of nitrogen dioxide drifting downwind from cities and power plants. By measuring the size and strength of these plumes, they calculated how much pollution was being emitted on the ground.
When the satellite-based estimates were compared to commonly used global and regional emissions inventories, the differences were large. In some cases, official databases overestimated pollution levels. In others, they underestimated them–sometimes by as much as six times.
“Our top-down emissions exhibit large, up to six-fold, systematic differences with contemporary global and regional inventories,” the researchers wrote.
To test their findings, the team updated an air-quality computer model using their satellite-derived emissions data. The updated model matched real satellite observations much more closely than models using standard emissions databases. According to the study, the model’s error rate was reduced by more than half after the adjustments.
For South African coal power plants—where direct ground-based emissions monitoring exists—the satellite estimates were within about 8% to 20% of official measurements, suggesting the method is reliable.
The authors say it’s important for independent monitoring in regions where ground-based data are limited. Accurate emissions information is critical for designing air quality regulations and public health policies.
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