Analytical Study of Atmospheric Boundary Layer Dynamics Over Lagos and Their Influence on Air Pollution Dispersion

The atmospheric boundary layer (ABL) in Lagos Metropolis controls the vertical mixing of pollutants emitted from transportation, industrial, and domestic combustion sources, yet ABL dynamics in this complex coastal megacity environment remain poorly characterized. This study analytically investigates ABL structure and dynamics over Lagos and their influence on air pollution dispersion using a combination of radiosonde ascent data from Lagos Airport, ERA5 reanalysis derived ABL height estimates, and concurrent PM2.5 concentration measurements at five monitoring sites across Lagos Metropolis for 2022 to 2023. ABL height was derived from radiosonde profiles using the bulk Richardson number method and validated against parcel method estimates. Diurnal and seasonal ABL height cycles were correlated with PM2.5 concentration time series using cross-correlation analysis. Results demonstrate that morning ABL heights below 200 metres in the November to January dry season create shallow mixing volumes that concentrate PM2.5 to levels exceeding 120 micrograms per cubic metre at traffic-adjacent monitoring sites. The nocturnal low-level jet, documented in 64 percent of dry-season radiosondes, is identified as a mechanism for transporting pollutants from industrial zones in the Lagos mainland to residential areas in Lagos Island during the pre-dawn hours. Coastal sea breeze dynamics complicate the midday dispersion pattern, generating a recirculation zone over Apapa industrial district. The study provides a physically grounded basis for improved air quality forecasting in Lagos. Keywords: atmospheric boundary layer, air pollution, Lagos, dispersion, PM2.5.