Source-Receptor Relationships and Cluster Analysis of CO2, CH4, and CO Concentrations in West Africa: The Case of Lamto in Cote d'Ivoire

The contribution in terms of long-range transport of CO2, CH4, and CO concentrations to measurements at Lamto (5 degrees 02 ' W-6 degrees 13 ' N) was analyzed for the 2014-2017 period using the FLEXPART model that calculates the retro-plumes of air masses arriving at the station. The identification of the source-receptor relationships was also studied with a clustering technique applied on those retro-plumes. This clustering technique enabled us to distinguish four categories of air mass transports arriving at Lamto site described as follows: oceanic and maritime origin (approximate to 37% of the retro-plumes), continental origin (approximate to 21%), and two hybrid clusters (approximate to 42%). The results show that continental emission sources contribute significantly to the increases in concentrations of CO2, CH4, and CO and explain approximate to 40% of their variance. These emission sources are predominantly from north and north-east directions of the measurement point, and where densely populated and economically developed areas are located. In addition, the transport of air masses from these directions lead to the accumulation of CO2, CH4, and CO. Furthermore, the ratios Delta CO/Delta CH4 and Delta CO/Delta CO2 observed in the groups associated with Harmattan flows clearly show an influence of combustion processes on the continent. Thus, the grouping based on FLEXPART footprints shows an advantage compared to the use of simple trajectories for analyzing source-receptor relationships.