Using pre-monsoon rainwater chemistry to monitor local atmospheric pollution in Kumasi, Ghana

Abstract

Rainwater chemistry offers a valuable tool for atmospheric pollution monitoring in urban environments where air quality is a growing concern. This work evaluated the composition of rainwater in Kumasi, Ghana, during the pre-monsoon season (February to April 2024), focusing on key ions such as SO₄²⁻, NO₃⁻, NH₄⁺, and Cl⁻. Rainwater samples were collected from Sokoban (a peri-urban area with localized industrial activities) and KNUST (an urban area) and analyzed for ionic composition. Enrichment factors (EFs) and neutralization factors (NFs) were used to determine pollutant sources (marine, crustal, or anthropogenic) and to evaluate the acid-neutralizing capacity of the rainwater. The results support a conglomerate influence of seasonal dust and anthropogenic activities relating to vehicular emissions and biomass burning, with high nitrate (NO₃⁻) concentrations. Local meteorology correlated variably with ion concentrations, with rainfall showing a strong negative correlation with pH (r = −0.97/−0.58) indicative of acidification. Maximum temperatures correlated positively with conductivity and turbidity, suggesting enhanced ion concentrations via evaporation under warmer conditions. Wind speed enhanced aerosol resuspension, while solar radiation correlated with higher nitrate concentrations, indicating enhanced photochemical reactions. The results highlight a rainwater chemistry-inspired framework to develop guidelines for urban air quality management.