Local pollution challenges in the global energy transition: air quality near hydrometallurgical and pyrometallurgical plants in the Congolese Copperbelt

The Congolese Copperbelt is a major source of copper and cobalt for the global energy transition, but mineral processing creates substantial and poorly documented local air-pollution risks. This study presents a multi-pollutant, multi-directional, and seasonally resolved assessment of ambient air quality around one hydrometallurgical plant in Kakanda and one pyrometallurgical plant in Lubumbashi. We monitored SO₂, NO₂, PM 10 , PM 2.5 , total suspended particles (TSP), Cu, and Pb during four campaigns in 2022, along with meteorological conditions and Air Quality Index (AQI) calculations. Most mean concentrations were below Congolese regulatory limits, although SO₂, Cu, and Pb showed episodic exceedances. By contrast, SO₂, NO₂, PM 10 , and PM 2.5 frequently exceeded the 2021 WHO health-based guidelines. Raw peak concentrations reached 6.0 mg/m 3 for SO₂ in the northern sector of the hydrometallurgical site and 5.0 mg/m 3 for NO₂ in the northern sector of the pyrometallurgical site. SO₂ dominated at the hydrometallurgical site, whereas NO₂ dominated at the pyrometallurgical site, consistent with the respective process profiles. The most severe conditions occurred in July, at the peak of the dry season, when the eastern sectors reached AQI values of 373.20 (Hazardous; SO₂-driven) at the hydrometallurgical site and 239.93 (Very Unhealthy; NO₂-driven) at the pyrometallurgical site. Lower relative humidity was associated with higher gaseous-pollutant concentrations, while stronger winds transported plumes toward northern and eastern sectors. These findings indicate that compliance with current Congolese limits does not necessarily provide health protection and support tighter standards, continuous monitoring, and process-specific emission controls. The local costs of the global energy transition are varied and are disproportionately borne by communities adjacent to mineral extraction and processing facilities.