Physicochemical quality and emission characteristics of artisanal‑refined diesel in the Niger Delta region of Nigeria and their air quality implications

This study provides a novel integrated assessment linking the physicochemical properties of artisanal-refined diesel in the Niger Delta region to its combustion emission behaviour. Diesel samples from 30 refining sites in Bayelsa and Rivers States were analysed using ASTM methods, and emissions (CO, NO x , SO₂, HC and CO₂) were quantified under controlled combustion conditions. The fuels exhibited significant deviations from regulatory standards, including elevated sulphur content (0.008%wt), high final boiling point (396.3 °C), increased ash content (0.02%wt) and Conradson carbon residue (0.16%wt), and a low cetane index (37.9%). Combustion emissions revealed substantial emission profiles, with CO ranging from 22.37–210.96 mg/m³ (mean 44.70 mg/m³), HC from 57–1101 mg/m³ (mean 470 mg/m³), NO x from 0.80–6.15 mg/m³ (mean 3.32 mg/m³), SO₂ from 2.13–4.22 mg/m³ (mean 3.37 mg/m³), and CO₂ from 1896 ̶ 2580 mg/m³ (mean 2063 mg/m³). CO and HC exceeded FEPA, WHO, World Bank and EGASPIN limits, producing hazardous AQI values of 447 and 940, respectively. Correlation analysis revealed weak relationships (|r| ≤ 0.278) between individual fuel properties and emissions, suggesting dominant multivariate effects. Compared with licensed refinery diesel, artisanal diesel produced substantially higher CO and HC emissions, highlighting significant environmental and public health concerns associated with its widespread utilisation in the Niger Delta.