Current Journal of Applied Science and Technology

As part of the INDAAF program, this study analyzes the variation in total aerosol (without size differentiation) ion masses, PM₂.₅, and PM₁₀ along a transect of African ecosystems ranging from dry savanna to equatorial forest. Weekly samples were collected between 1996 and 2009 at five sites: Banizoumbou (Niger), Katibougou (Mali), Lamto (Ivory Coast), Zoetele (Cameroon), and Djougou (Benin). Inorganic ions (Cl⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺) and organic ions (HCOO⁻, CH₃COO⁻, C₂H₅COO⁻) were quantified by ion chromatography. The results reveal a negative gradient in the total ionic mass of aerosols during the dry season, ranging from 9.10 µg/m³ in Banizoumbou to 4.58 µg/m³ in Zoetele. These values are 1,78 to 3.47 times higher than those obtained during the wet season. This gradient is controlled by the temperature gradient and the gradient of the species concentrations established along the ecosystem transect. Significant correlations (p < 0.001) show a dominance of terrigenous sources in dry savannas (Ca²⁺: R = 0.97 in Banizoumbou; R = 0.95 in Katibougou), while biogenic emissions predominate in wet savannas (K⁺ in Lamto, R = 0.94) and equatorial forest (SO₄²⁻ in Zoetele, R = 0.81). CO₃²⁻ contributes significantly to the ionic mass of aerosols: up to 44% in the dry season at Banizoumbou, compared to 7.8% in Zoetele. In Djougou, PM₁₀ correlates with C₂O₄²⁻    (R = 0.98, p < 0.025), while PM₂.₅ correlates with K⁺ (R = 0.94, p < 0.001) and (Ca²⁺ + NH₄⁺). In Banizoumbou, PM₁₀ correlates with Ca²⁺ (R = 0.99, p < 0.001), and PM₂.₅ with (Ca²⁺ + NH₄⁺) (R = 0.97, p < 0.005). These observations confirm the predominance of terrigenous inputs in arid areas and biogenic emissions (biodegradation, biomass fires) in wet areas.