Black carbon and elemental composition of PM2.5 aerosol in Ghana: Concentrations, correlation and health risk assessment in urban neighbourhoods

PM2.5 (particles with aerodynamic diameter less than or equal to 2.5 µm) has a strong ability to adsorb elemental species due to its small size. This study aimed to determine the elemental and black carbon (BC) concentrations and the health risks associated with exposure to PM2.5-bound species in Apam, an urban area characterised by wood-burning, and at the Winneba highway intersection (WHI) in Ghana. A Gent sampler, equipped with a Gast pump and a stacked filter unit, was utilised to collect airborne particulates. Sampling occurred three times per week from July 2022 to June 2023, with each session lasting 24 hours. The particulate samples were analysed for elemental and BC concentrations using an Ag-anode X-ray tube spectrometer and a smoke stain reflectometer, respectively. The US EPA health risk evaluation model assessed the health hazards associated with trace elements. The study found that the average concentrations of Ni (76.51 ng/m³) and Cr (61.66 ng/m³) at WHI, and Ni (111.36 ng/m³) and Cr (78.42 ng/m³) at Apam, exceeded the US EPA threshold limits. The enrichment factor model indicated that S, Cl, Cr, Ni, Zn, Cu, Pb, and Br originated from anthropogenic sources, whereas Na, Mg, Al, Si, Ti, Ca, V, Sc, Rb, and Sr were derived from natural sources. BC showed a strong correlation with potassium (r>0.79), suggesting their release from biomass burning. A significant relationship (r>0.60) was observed among BC, S, Pb, Ni, and Cu at WHI, indicating their substantial release from vehicular emissions. The overall cancer risk levels for exposure to PM2.5-bound species via ingestion and dermal contact exceeded 10-4, indicating potential cancer risks. Implementing eco-friendly transportation and using clean fuel are necessary to mitigate PM2.5 and its associated health concerns