Source Apportionment of Ambient Particulate Matter (PM) in Two Western African Urban Sites (Dakar in Senegal and Bamako in Mali)

Following population growth and rapid urbanization, West African cities have become major sources of anthropogenic pollution. Additionally, Saharan dust has had a significant impact, representing a potentially toxic mix of sources for the population. This study characterizes the atmospheric composition and its sources in two African capitals, Bamako, Mali and Dakar, Senegal. TSP, PM10 and PM2.5 samples were collected during the dry season in 2009 when pollution levels were high: chemical analysis included organic carbon (OC), elemental carbon (EC), ions, and metals. PM2.5 and PM10 concentrations were 5-10 times and 3-8 times higher, respectively, than the 2005 WHO 24 h standards. Using PCA and PMF methodologies, five sources were identified in each city. In Bamako, traffic (motor vehicles and resuspended road dust) was the prevailing source of PM2.5 and PM10, accounting for 47% and 45%, respectively. Crustal dust was the second most important source (24-30%), followed by solid fuel combustion (16-13%) and secondary aerosols (10-16%). In Dakar, the following sources of PM2.5 and PM10 are identified: traffic (49%), mineral dust (16-25%), sea salts (15-20%) and industries (10-11%). Our study provides crucial information about the historical change in source characteristics in these two African cities, which can help for future mitigation strategies.