Trace Element categorization of pollution sources in the Equator town of Nanyuki, Kenya

Abstract

An air pollution campaign was carried out in the town of Nanyuki at four different sites during July and August 1999. Nanyuki is situated on the equator on the northwestern slope of Mount Kenya at about 1930 m above sea level.

The intention of the project was to characterize aerosol elemental compositions in two size fractions, associated with specific natural and anthropogenic activities. A dichotomous impactor was used for sampling and an energy-dispersive x-ray fluorescence spectrometer was used for the analysis. Fourteen elements (Si, S, K, Ca, Ti, Mn, Fe, Cu, Zn, Ga, Br, Rb, Sr and Pb) were analysed in all the samples.

The concentration of Pb was highest at a site in the vicinity of open-air vehicle garages. The four sites recorded high concentrations of fine S, Cl and K. Fine Zn and Br were also measured at all the sites. In the coarse size range, the concentrations of soil-derived elements (Si, K, Ca and Fe) were dominant.

The high concentration of coarse Cl was considered to be due to the contribution of sea salt and that of S to be a contribution of gas to particle conversion of S02' The two elements Sand CI signified the influence of long-distance transported aerosols.

The comparatively high concentrations of fine Pb and Br signified the high rate of vehicle repairs, which is a major activity close to one of the sites. Generally, soil dust-derived particles and those from biomass burning dominated the town aerosols.