Trace Metals and Source Identification of Air-Borne Particulate Matter Pollution in A Nigerian Megacity

Abstract

Background: The megacity status of Lagos has led to increased pressure on the urban environment especially on air quality. Twelfth decade of serving as Nigeria former capital and currently the economic nerve centre of the country, there is yet no holistic information on source apportionment of atmospheric aerosols in the city. Hence, the study was conducted to provide an understanding of the chemical compositions and source identifications of PM2.5 (aerodynamic diameter, dae ≤ 2.5 μm) and PM2.5-10 (2.5 μm<dae<10 μm) particulate matter over Lagos, Nigeria. Methods: Sampling of PM2.5 (fine) and PM2.5-10 (coarse) were collected on nuclepore polycarbonate filters using a low volume GENT sampler (Schlumberger Model: M250) equipped with double staged stacked filter units. A total of 192 samples were collected (96 of each fraction). Elemental analyses of both fractions were carried out using Particle Induced X-ray Emission (PIXE) while Proton Induced Gamma-ray Emission (PIGE) was also employed to complement for X-ray self-absorption effect among low Z elements by PIXE technique. Results: Data on twenty-four elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Se, Br, Rb, Sr, Zr, Cs and Pb) detected in both particulate sizes were displayed, discussed. Receptor modelling of the data for source apportionment and identification were achieved for both fractions via positive matrix factorization (PMF). Five source categories with stable profiles were identified in both fractions. Conclusions: The study concluded that anthropogenic emissions from gasoline oil combustions, industrial, and biomass burning emissions were more predominant and could pose great hazard to Lagos receptors during the sampling period.