Spatial and seasonal analysis of traffic-related pollutant concentrations in Lagos Metropolis, Nigeria.

Abstract

Leaf samples of Terminalia catappa L (Almond) trees dominant in Lagos metropolis, Nigeria were collected from 34 sampling points located within dominant land-uses (commercial, residential, industrial, institutional, acquisition/parks, dumpsites/incinerators and transportation) along traffic corridors and six stations located 250 m away (as control) during the short wet and short dry seasons for two years. Concentration of trace elemental pollutants: (Pb, Cd, Cu, Cr, Al, Zn, As, Hg, Fe, Mn, Mg) were determined by laboratory analyses of leaf samples. Multivariate analysis was used to test for significant geographical and seasonal variations in air pollutants. Total suspended particulate matter varied from 22.36 - 29.07 mg/m3 against WHO Air Quality Standard (AQS), 0.05 - 0.15 mg/m3; Sulphur-dioxide and Ozone varied from 1.1 - 1.73 mg/m3 and 0.01 - 0.18 mg/m3 respectively as against 0.00125 and 0.0015 mg/m3 AQS. ANOVA showed spatio-temporal variations in pollutants and significant correlation of traffic density with all metals studied (P < 0.05). Lead varied from 1.4 - 3.1 mg/m3 and 1.7 - 2.6 mg/m3, Cadmium varied from 1.7 - 3.15 mg/m3 and 0.011 - 0.1 mg/m3, Iron varied from 3.06 - 3.6 mg/m3 and 0.5 - 2.6 mg/m3, while Arsenic varied from 0.9 - 1.98 mg/m3 and 0.011 - 0.1 mg/m3 along traffic corridors and at control points respectively. Step-wise regression analyses further showed that traffic density, air temperature and land-use contributed significantly to air pollution (P < 0.05). The micro-climate of Lagos metropolis is characterised by relatively high air temperature, low wind speed and air pollution that varied according to traffic density and land-use. Concentrations of pollutants were higher than the WHO Air Quality standards and were also higher along traffic corridor than further away. Key words: Lagos metropolis, air pollution, bio-monitoring, traffic density, land-use.