IBA characterisation and source apportionment of fine and coarse particulate matter in Accra, Ghana (Metadata RADIATE TA Proposal 21002549-ST)

Proposal title "IBA characterisation and source apportionment of fine and coarse particulate matter in Accra, Ghana". Measurements carried out at the external beam set-up for atmospheric aerosol analysis of the INFN LABEC accelerator laboratory, from 6 till 9 June 2022. Hands-off mode.

Accra, the capital city of Ghana with over five million habitants, is still a developing city. Like many cities in developing countries, Accra is faced with environmental challenges such as domestic waste incineration, open e-waste burning, dust from construction activities and some unpaved roads, emissions from industries and vehicular exhaust in congested road traffic. Though there are air quality monitoring activities in Accra, they are mainly limited to air particulate loads assessment.  This is due to lack of adequate tools to carry out chemical compositions that will lead to pollution source identification and apportionment to help policy decision making on environmental issues.

Two size fractions (PM_2.5and PM_2.5-10) of atmospheric aerosol samples were collected on 47 mm diameter nucleopore filters using a Gent Sampler at a flow rate of 1 m³/hr. The sampling campaign consisted of 24 hours of continuous sampling on each sampling day between 2014 to 2019.  A total of 600 (300 each of coarse and fine) loaded filters were obtained from three monitoring stations in Accra. These samples were measured by PIXE technique using a proton beam of 3 MeV energy with a few tens nA intensity to determine their elemental composition.

Elemental concentrations of major elements such as Na, Mg, Al, Si, S, Cl, K, Ca, and Fe which are mostly fingerprint elements of soil dust and sea spray stood out for both fractions. The mean concentrations of these elements are relatively higher in the coarse fraction compared to their respective concentrations in the fine fraction. Conversely, fingerprints elements of anthropogenic sources tend to be higher in the fine fraction. Also, S and K show an important contribution in the fine fraction: S is indeed a typical secondary aerosol element while K, besides being a crustal element, is also produced by biomass burning.