Mass concentrations and elemental composition of urban atmospheric aerosols in Addis Ababa, Ethiopia

Abstract

Aerosol samples were collected from 22 February 2008 to 15 April 2008 and 17 June 2008 to 23 July 2008 in urban and peri-urban areas of Addis Ababa, Ethiopia, with the aim to assess the spatial and temporal aspects of total suspended particulate (TSP) and particulate matter with aerodynamic diameter less than 10 µm (PM₁₀) and their composition in terms of metallic elements. Sixty six filter samples were collected from seven distinct sites using I.O.M. multi fraction dust samplers and fiber glass filter papers. The mass of each particulate matter sample was measured gravimetrically and the composition of PM₁₀ samples was analyzed using ICP-OAES and SEM-EDAX. The concentration of TSP was in the range of 17-556 µg/m³ and that of PM₁₀ was in the range of 17-285 µg/m³. The highest TSP and PM₁₀ peak values were observed in February 2008 at two sites, whereas the lowest TSP and PM₁₀ values were observed in June and July 2008 at two sites. The mean TSP concentration surpassed the WHO safe guideline value of 150 µg/m³ and 79 % of the PM₁₀ values were below the WHO guideline value. The PM₁₀ to TSP mass ratio was in the range 0.26-0.59 and PM₁₀ mass contributed about 39% to the TSP mass. The average element concentration in PM₁₀ filter sample was in the order of Ca > Na > K > Zn > Sb > B > Al > V > Mg > S > Fe. All the analyzed elements contributed about 0.1% to the PM₁₀ mass. SEM-EDAX analysis of PM₁₀ samples showed that Si, Al, Na, Zn, Ba, K and C were the predominant species. Crustal materials contributed 76-95% of the filter mass, and C and Cu represented 5-24%. The size distribution of aerosol particles as derived from SEM analysis was in 0.43-9.3 µm range.

KEY WORDS: TSP, PM₁₀, Metal analysis, Atmospheric aerosol, Addis Ababa, Ethiopia

Bull. Chem. Soc. Ethiop. 2010, 24(3), 361-373.