An air quality assessment in the industrialised western Bushveld Igneous Complex, South Africa

Abstract

South Africa has the largest industrialised economy in Africa, with significant mining and metallurgical activities. A large fraction of the South African mineral assets is concentrated in the Bushveld Igneous Complex (BIC), with the western limb being the most exploited. Because the majority of the world's platinum is produced in the BIC, this area is also of international interest. There are some indications that the western BIC should be considered an air pollution hotspot; however, inadequate data exist to substantiate these claims scientifically. To partially address this knowledge gap, a comprehensive air quality monitoring station was operated for more than 2 years in this area. Meteorological parameters, trace gas concentrations and total mass concentration of particulate matter up to 10 µm in size (PM₁₀) were measured. Compared with South African and European ambient air quality standards, SO₂, NO₂ and CO concentrations were generally acceptable. The major sources of SO₂ were identified as high-stack industry emissions, while household combustion from semi-formal and informal settlements was identified as the predominant source of NO₂ and CO. In contrast, O₃ exceeded the 8-h moving average more than 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-h standard 6.6 times per year, the future (2015) standard 42.3 times per year and the European standard more than 120 times per year. The main source of PM₁₀ was identified as household combustion from semi-formal and informal settlements. The findings clearly indicate that atmospheric O₃ and PM₁₀ levels in the western BIC need to be addressed to avoid negative environmental and human health impacts.