The Total PM2.5, Chemical Composition and Geographical Origin of Air Masses in a Legacy Mining Town, Welkom, South Africa

This study investigated fine particulate matter (PM2.5) in Welkom, South Africa, a legacy mining town. PM2.5 was sampled over 12 months at two sites, an Industrial Site and a Residential Site located only 5.6 km apart, to assess total concentrations, PM2.5 chemical composition, soot, black carbon (BC), UV-absorbing particulate matter (UV-PM), and the geographical origin of air masses. At the Industrial Site, the annual mean PM2.5 concentration was 14.7 µg/m³ (0.17–66.3 µg/m³), while the Residential Site recorded a markedly lower mean of 6.47 µg/m³ (0.17–24.3 µg/m³). Mean soot levels were 1.07 × 10−5 m−1 (0.01–5.52 × 10−5 m−1) at the Industrial Site and 1.10 × 10−5 m−1 (0.014–5.50 × 10−5 m−1) at the Residential Site. BC concentrations averaged 1.9 µg/m³ (0.028–8.01 µg/m³) at the Industrial Site and 0.6 µg/m³ (0.2–2.8 µg/m³) at the Residential Site. UV-PM averaged 1.6 µg/m³ (0.006–5.22 µg/m³) at the Industrial Site and 0.8 µg/m³ (0.1–3.1 µg/m³) at the Residential Site. Clustered back-trajectory analysis further showed that northerly and easterly air masses carried the highest PM2.5, soot, BC, and UV-PM levels. Across all pollutants, higher concentrations at the Industrial Site highlight the influence of local combustion sources, resuspended dust, and industrial activities.