Physicochemical Characterization of Air Pollution Particulate Matter (PM2.5 and PM>2.5) in an Urban Area of Cotonou, Benin

PM2.5 and PM>2.5 samples were collected in Cotonou (Benin) using high volume cascade impaction air samplers. The samplings were based on continuous collection over twelve days. Physical and chemical characteristics of samples were determined by size distribution (laser granulometry), specific surface areas (BET method), inorganic elements (ICP-MS), water-soluble ions (IC), CHNS analysis and organic compounds (GC-MS). Average concentrations of air particulate matter were 180.9 mu g/m(3) and 94.5 mu g/m(3) in PM2.5 and PM>2.5, respectively. The higher water-soluble ions recorded were Ca2+,SO42-,NO3-, Na+ and Cl- for both PM. Moreover, concentrations were almost two-fold higher for PM2.5 compared to PM>2.5, with 10.7 mu g/m(3) of total metals found in PM2.5 versus 5.6 mu g/m(3) in PM>2.5. Both PM samples under study presented similar repartition of elements considering their percentages. Results suggested that PM>2.5 samples contain agglomerates of fine particles. Identification tools of major pollution source as inorganic elements, paraffins, fatty acids ratios and PAHs ratios indicated that PM under study originated from traffic exhaust.

Automated summary

This study collected PM2.5 and PM2.5-10 samples in Cotonou, Benin, using high volume cascade impaction air samplers for twelve days. The physical and chemical characteristics of the samples were analyzed by various methods including size distribution analysis, specific surface area measurement, inorganic element analysis, water-soluble ion analysis, and organic compound analysis. The results showed that the average concentrations of PM2.5 and PM2.5-10 were 180.9 μg/m³ and 94.5 μg/m³, respectively. The major water-soluble ions in both types of particulate matter were Ca2+, SO42-, NO3-, Na+, and Cl-. The concentrations of total metals in PM2.5 were nearly two times higher than in PM2.5-10. The analysis of major pollution sources indicated that the PM originated from traffic exhaust.