Characterizing air pollution in two low-income neighborhoods in Accra, Ghana

Abstract

Sub-Saharan Africa has the highest rate of urban population growth in the world, with a large number of urban residents living in low-income “slum” neighborhoods. We conducted a study for an initial assessment of the levels and spatial and/or temporal patterns of multiple pollutants in the ambient air in two low-income neighborhoods in Accra, Ghana. Over a 3-week period we measured (i) 24-hour integrated PM 10 and PM 2.5 mass at four roof-top fixed sites, also used for particle speciation; (ii) continuous PM 10 and PM 2.5 at one fixed site; and (iii) 96-hour integrated concentration of sulfur dioxide (SO 2) and nitrogen dioxide (NO 2) at 30 fixed sites. We also conducted seven consecutive days of mobile monitoring of PM 10 and PM 2.5 mass and submicron particle count. PM 10 ranged from 57.9 to 93.6 μg/m 3 at the four sites, with a weighted average of 71.8 μg/m 3 and PM 2.5 from 22.3 to 40.2 μg/m 3, with an average of 27.4 μg/m 3. PM 2.5/PM 10 ratio at the four fixed sites ranged from 0.33 to 0.43. Elemental carbon (EC) was 10–11% of PM 2.5 mass at all four measurement sites; organic matter (OM) formed slightly less than 50% of PM 2.5 mass. Cl, K, and S had the largest elemental contributions to PM 2.5 mass, and Cl, Si, Ca, Fe, and Al to coarse particles. SO 2 and NO 2 concentrations were almost universally lower than the US-EPA National Ambient Air Quality Standards (NAAQS), with virtually no variation across sites. There is evidence for the contributions from biomass and traffic sources, and from geological and marine non-combustion sources to particle pollution. The implications of the results for future urban air pollution monitoring and measurement in developing countries are discussed.