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

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 PM10 and PM2.5 mass at four roof-top fixed sites, also used for particle speciation; (ii) continuous PM10 and PM2.5 at one fixed site; and (iii) 96-hour integrated concentration of sulfur dioxide (SO2) and nitrogen dioxide (NO2) at 30 fixed sites. We also conducted seven consecutive days of mobile monitoring of PM10 and PM2.5 mass and submicron particle count. PM10 ranged from 57.9 to 93.6 μg/m3 at the four sites, with a weighted average of 71.8 μg/m3 and PM2.5 from 22.3 to 40.2 μg/m3, with an average of 27.4 μg/m3. PM2.5/PM10 ratio at the four fixed sites ranged from 0.33 to 0.43. Elemental carbon (EC) was 10–11% of PM2.5 mass at all four measurement sites; organic matter (OM) formed slightly less than 50% of PM2.5 mass. Cl, K, and S had the largest elemental contributions to PM2.5 mass, and Cl, Si, Ca, Fe, and Al to coarse particles. SO2 and NO2 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.