Source apportionment of PM2.5 pollution in Lagos, Nigeria

Abstract

This study presents a source apportionment of fine particulate matter (PM2.5) in the megacity of Lagos, Nigeria. The study took place from the beginning of January to the middle of March 2025, encompassing air pollution during the months of the dry season, characterised by Harmattan winds. The aim was to explore the level of PM2.5 and to better understand the air pollution in Lagos by doing source apportionment. A total of sixty 24-hour filters were collected by people at the University of Lagos and sent to Gothenburg. The PM2.5 was determined gravimetrically, and the elemental composition was analysed using an optical transmissometer and an Energy Dispersive X-Ray Fluorescence (EDXRF) instrument. The resulting data were then analysed through correlation analysis and by performing Positive Matrix Factorisation on the data for the source apportionment. Twenty-two elements were detected and quantified: Al, P, S, Cl, K Ca, Ti, V, Mn, Fe, Cu, Zn, Ga, As, Se, Br, Sr, Y, Ba, Hg, Pb, and Si, along with black carbon (BC) and ultraviolet absorbing particulate matter (UVPM). The average PM2.5 level was found to be 37 ± 24 µg/m³, exceeding the WHO 24-hour guideline of 15 µg/m³. Identified sources included mineral dust, combustion of petroleum products and vehicular emissions, biomass burning, sea salt, steel industry, and a V-rich source. Among these, mineral dust and the factor for combustion of petroleum products + vehicular emissions were the dominant contributors to PM2.5 mass. There was a discrepancy between the reconstructed mass and the total mass of PM2.5, suggesting that additional PM2.5 components not detectable by the instruments used may also be present. Improvements for further studies would be to have a larger data set, include meteorological data, and a broader range of chemical species to improve source identification and mass reconstruction.