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Characterization and source identification of airborne particulate loadings at receptor site-classes of Lagos Mega-City, Nigeria

Size segregated suspended particulate matter (PM2.5 and PM2.5-10) were collected using Gent low-volume air sampler at four different receptor site-classes in Lagos Mega City, Nigeria. The particulate mass loading was quantified and the concentration was analyzed to examine the pattern and variation from one receptor site-class to another. The PM2.5/PM10 ratio varied among the site-classes with the residential and marine sites having the least and highest ratio of 0.31± 0.13 and 0.49 ± 0.17 respectively. Particulate loading was higher on weekdays than on weekends (by a factor of about 1.5) in all but the marine site-class.The mean PM2.5/PM10 ratio is 0.41 ± 0.15, which suggests that traffic emission is not the principal source of the Particulate Matter (PM). The INAA assay of the particulates detected ten elements: As, Br, Ce, K, La, Mo, Na, Sb, Sm and Zn. Except for Br, Mo and Sb, the detected elements were more pronounced in the coarse-fractioned filter. Principal Component Factor Analysis (PCFA) of the detected elements identified some common sources (traffic-related, traffic emission, sea-salt and industrial emission) for both PM fractions at the four receptor site-classes. Implications: An assessment of the ambient air quality of the study area has been carried out. Some residential areas can have high particulate matter (PM) loading even more than industrial areas due to contributions from local and transport from neighboring sites. The site-classes have common PM sources and PM loadings are generally lower on weekends than on weekdays, with the coarse fraction being dominant. Measures should be put in place to reduce contributions to PM loading by biomass burning, traffic-related, and industrial emissions, as they have been identified as common and prominent anthropogenic sources of PM.