Spatial Analysis of Ambient Air Quality Gradients in Lagos Using Low-Cost Sensor Networks

This study employs a dense network of calibrated low-cost air quality sensors to empirically characterise the spatial and temporal gradients of PM2.5 and nitrogen dioxide concentrations across Lagos, South West Nigeria, addressing the critical gap in high-resolution urban air quality data in Nigeria's most populous city. Official fixed monitoring stations in Lagos are too few and too widely spaced to resolve the fine-scale pollution gradients created by traffic corridors, industrial zones, generator clusters, and market areas, limiting the evidence base for targeted air quality management. A network of forty-eight low-cost electrochemical and optical sensors was deployed across Lagos for twelve months, with instrument co-location tests against reference methods used to develop correction factors and uncertainty bounds. Spatial interpolation using ordinary kriging was applied to produce continuous air quality maps at 500-metre resolution. Temporal analysis examined diurnal, weekly, and seasonal patterns. Regression analysis identified the land use, traffic density, and generator cluster density variables most strongly associated with elevated concentrations. Results show a highly heterogeneous spatial distribution with PM2.5 hotspots at market areas, generator-dense commercial streets, and road intersections, exhibiting concentrations two to four times higher than background residential levels. Residential areas show a pronounced nocturnal PM2.5 peak from neighbourhood generator use. The study provides the highest-resolution air quality dataset yet produced for Lagos. Findings identify specific high-exposure zones where health-protective interventions should be prioritised. Keywords: low-cost sensor, spatial air quality mapping, Lagos, PM2.5, nitrogen dioxide.