Characterization of aerosol particles at an industrial background site in Nairobi, Kenya.

Abstract

Air pollutants from industrial sources contain harmful elements and chemical compounds. This work presents a study on background industrial and urban aerosol particles in the city of Nairobi. Its main focus was the understanding of elemental, black carbon (BC) and particulate mass (PM) concentrations in the perspective of identifying their sources. Aerosol particles were collected on Teflon filters in two size fractions, a fine fraction of particles having an aerodynamic diameter (da) < 2.5 m and a coarse fraction with particles between 2.5 m and 10 m. A photometer and an Energy Dispersive X-Ray Fluorescence spectrometer were used to analyze BC and trace elements (Si, S, Cl, K, Ca, Ti, V, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, and Pb), respectively. The sampled mass of the particulate matter was determined gravimetrically. The measured concentrations of the analysable species were dominated by BC, K, and S in the fine fraction and Si, Ca, and Fe in the coarse fraction. Principal component analysis and correlation evaluation of the fine fraction concentrations implicated industrial, vehicular, and biomass burning emissions as the main sources of the measured elements. The average Pb concentration of 105 ng m-3 in the PM10 sample at the background industrial site is approximately 20% of the Air Quality Guideline (AQG) recommended by World Health Organisation (WHO). Most of the measured elements exhibited higher concentrations than those measured in Francistown in Botswana, Dar es Salaam in Tanzania and Edinburgh in United Kingdom but less than those measured in Barcelona in Spain and from previous studies in Nairobi.