The Chemical Characteristics of Rainwater and Wet Atmospheric Deposition Fluxes at Two Urban Sites and One Rural Site in Cote d'Ivoire

Due to their close relationship with atmospheric chemical composition and global impacts on ecosystems, it is of crucial importance to determine rain chemical composition and quantify wet deposition. In this study, we characterized the chemical composition of precipitation at one rural and two urban sites in Cote d'Ivoire along a south-north transect. Annual and monthly Volume Weighted Mean (VWM) concentration of major ions, as well as wet deposition fluxes in rainwater samples from Abidjan, Korhogo (urban sites), and Lamto (rural site), have been calculated. We also simulated air mass back-trajectories and generated satellite maps of burnt fraction and nitrogen species emissions (NH3, NO2) to better analyze our results. Results show that the dominant ion at both urban sites is Ca2+, whereas NH4+ dominates the chemical content of the Lamto rural site. The analysis of atmospheric sources of influence shows that urban sites rains are characterized by a mixture of terrigenous continental and anthropogenic sources (39-33%), as well as a high marine contribution (34-24%) and a significant nitrogenous contribution (18-25%) mainly associated to fossil fuel from road traffic, domestic and biomass burning sources. At the rural Lamto site, marine, terrigenous, and nitrogenous contributions represent, respectively, 14%, 25%, and 30%. The average pH values are, respectively, 5.76, 5.31, and 5.57 for Abidjan, Lamto, and Korhogo, with a preponderance of mineral acidity contribution at the urban sites, while the organic acidity contribution dominates in Lamto. Neutralization factor (NF) of mineral and organic acids calculations revealed that Ca2+ and NH4+ are the most important neutralizing ions in the rain at all three sites, and we estimated that 79% to 87% of the rain acidity is neutralized by alkaline compounds.

Automated summary

In this study, precipitation samples were collected at one rural and two urban sites in Cote d'Ivoire, and the chemical composition and wet deposition fluxes were analyzed. Results showed that Ca2+ was the dominant ion in urban areas, while NH4+ was dominant in rural areas. The analysis of atmospheric sources revealed that urban areas were influenced by a mixture of terrigenous continental, anthropogenic, marine, and nitrogenous sources, while rural areas were mainly affected by marine, terrigenous, and nitrogenous sources. The evaluation of rain acidity showed that alkaline compounds were responsible for neutralizing a significant portion of the acidity.