The chemical characteristics of rainwater and wet atmospheric deposition fluxes at two urban sites and one rural site in Côte d’ Ivoire

Abstract. In this study, we characterized the chemical composition of precipitation at three sites in Côte d'Ivoire representative of a south-north transect. Two urban sites have been selected in the framework of the Pollution and Health in Urban Areas (PASMU) project: one located in Abidjan in the coastal climate zone and the other located in Korhogo in the northern climate zone. The third site is the International Network to study Deposition and Atmospheric chemistry in Africa (INDAAF) rural site of Lamto representative of a wet savanna and located in the central climate zone. This work documents a three-year time period (2018–2020) with 221 samples, 239 samples and 143 samples which have been collected in Abidjan, Lamto and Korhogo, respectively. Annual and monthly VWM concentration of major ions (Na+, K+, Mg2+, Ca2+, Cl-, NO3- SO42-, NH4+, HCOO-, CH3COO-, C2H5COO-, C2O42-) in rainwater have been calculated and were found to follow the following patterns: Ca2+> Cl-> Na+> NH4> SO42-> Tcarb > NO3-> Mg2+> HCOO- > CH3COO- > K+ > H+> C2O42-> C2H5COO- in Abidjan, NH4+ > HCOO- > Ca2+ > NO3-> CH3COO- >H+ > Cl- >Na+> SO42- > Mg2+ > K+ > Tcarb > C2O42- > C2H5COO- in Lamto and Ca2+ > NH4+ > Na+ > HCOO- > NO3- > Cl- > K+ > CH3COO- > SO42- > H+ > Mg2+ >Tcarb > C2O42- > C2H5COO- in Korhogo. The average pH values are respectively 5.76, 5.31, 5.57 for Abidjan, Lamto and Korhogo with a preponderance of mineral acidity at the urban sites representing respectively 69 % and 52 % of the total acidity contribution in Abidjan and Korhogo while the organic acidity is more important in Lamto representing 62 % of the total acidity contribution. Dry seasons contribute to 46 %, 74 % and 86 % to the total measured chemical content of precipitation respectively at Abidjan, Lamto and Korhogo. During dry seasons, Lamto and Korhogo rainfalls are more impacted by biomass burning source and continental air mass loaded in terrigenous compounds than Abidjan. Conversely, during wet seasons Abidjan rainfalls are more impacted by oceanic air mass from guinean gulf rich in sea salt than Lamto and Korhogo.