Comparison of measures of PM2.5 and carbonaceous aerosol in air at Cotonou, Benin in 2005 and 2015.

This study focuses on the comparison of carbonaceous aerosol measurements in the air at Cotonou in 2015 compared to 2005. In the framework of two international programs, AMMA (African Monsoon Multidisciplinary Analysis) and DACCIWA (Dynamics Aerosol-Cloud-Chemistry Interactions in West Africa) monitoring data for PM2.5 microns were collected at one of the most polluted urban site of Cotonou (Dantokpa) in Benin (West Africa) respectively in 2005 and 2015. The results obtained indicate that the carbonaceous aerosol measures, Black carbon (BC), and organic carbon (OC) in 2005 are higher than those obtained in 2015. PM2.5 concentrations related mainly to traffic sources for 2 wheeled vehicles, were 34g/m³ in May 2005 and 28µg/m³ in May 2015. In May 2005, OC and BC concentrations were from 15µg/m³ and 2.3µg/m³ while in May 2015, they were from 8µg/m³ for OC and 1.3 µg/m³ for BC. In May 2005 and 2015, the total carbon (TC) accounted for 50 % and 32 % of the PM2.5, respectively. In this study, the OC/EC ratio exceeds 2.0, which confirms the presence of secondary organic aerosols.