Spatiotemporal Variations in Ambient Air Quality During Flyover Construction in Effurun Metropolis, Delta State, Nigeria: Implications for Urban Public Health

Ambient air pollution remains a persistent urban health challenge, particularly in rapidly developing African cities where construction activities, dense traffic and mixed land use interact to elevate pollutant burdens. This study assessed the spatiotemporal variability of ambient air quality during the construction of three major flyovers in Effurun Metropolis, Delta State, to characterize pollutant dynamics and evaluate associated public-health risks. Eight pollutants (PM2.5, PM10, CO, NO2, SO2, H2S, CH4 and VOCs) were monitored at Effurun Roundabout, PTI Junction and DSC Roundabout over six months using calibrated portable analysers with measurements taken twice daily alongside real-time meteorological observations. Results showed marked spatial contrasts, with PM2.5 peaking at Effurun (54.85 μg/m3), PM10 highest at DSC (77.38 μg/m3), and exceptionally high CO concentrations at PTI (326.50 ppm) and DSC (271.90 ppm). Pollutant loads were greatest between February and April, driven by dry-season dust suspension and intensified mechanical activity, and declined with the onset of rainfall. AQI classifications indicated unhealthy conditions for PM2.5 and SO2 and Hazardous conditions for CO across all sites. These patterns indicate acute short-term exposure risks for residents, workers and road users, with implications for respiratory and cardiovascular health. The findings emphasise the need for real-time monitoring, strict machinery maintenance, low-Sulphur fuels, dust suppression and regulatory enforcement during major urban construction. Integrating air-quality safeguards into infrastructural planning will be essential for protecting public health as Nigerian cities continue to expand.