Air quality assessment of the industrialized western Bushveld Igneous Complex

Abstract

South Africa has the largest economy in Africa, with significant mining and metallurgical activities. A large fraction of the mineral assets is concentrated in the Bushveld Igneous Complex (BIC), with the western limb being the most exploited. Although the western BIC is considered to be an air pollution hotspot, inadequate air quality data currently exists for this area. To partially address this knowledge gap, a comprehensive air quality monitoring station was operated for more than two years at Marikana in the western BIC. Basic meteorological parameters, precipitation, Photosynthetic Photon Flux Density (PPFD), trace gas concentrations (SO2, NO, NOx, O3, and CO), physical aerosol parameters (particle number and air ion size distributions, as well as aerosol light absorption) and total PM10 mass concentration were measured. Compared with South African and European ambient air quality standards, SO2, NO2 and CO concentrations were generally below the air quality standards, with average concentrations for the sampling period of 3.8ppb (9.9μg/m³), 8.5ppb (15.9μg/m³) and 230ppb (270μg/m³), respectively. The major source of SO2 was identified as high-stack industry emissions, while household combustion was identified as the predominant source of NO2 and CO. In contrast, O3 exceeded the eight-hour moving average standard (61ppb / 120μg/m³) 322 times per year. The main contributing factor was identified to be the influx of regional air masses, with high O3 precursor concentrations. PM10 exceeded the current South African 24-hour standard (120μg/m³) on average 6.6 times per year, the future 2015 standard (75μg/m³) 42.3 times per year and the European standard (50μg/m³) 120.2 times per year. The PM10 average concentration for the sampling period was 44μg/m³, which exceeded the current European and future (2015) South African annual average standard (40μg/m³), emphasising the PM pollution problem in the western BIC. The main source of PM10 was identified as household combustion.