Concentration contextualisation, temporal patterns and sources of hydrogen sulphide at a site on the South African Highveld

Abstract

South Africa is one of the largest atmospheric sulphur emitting countries, but the contribution of H2S to this regional burden is not known. Also, no H2S source apportionment for South Africa have been undertaken, although H2S has adverse effects on the environment and human health both directly and after being oxidised. Measurements were conducted for 2 years at a site on the Mpumalanga Highveld (South Africa), which is influenced by multiple sources. A mean of 3.1 ppb H2S was obtained, which is similar than concentrations reported for some large Northern Hemisphere cities and areas close to gas processing plants. Well defined seasonal and diurnal patterns indicated that low-level emission sources likely made a significant contribution to the ambient H2S concentrations. In this study, a receptor method was developed to enable identification of sources and quantification of their contribution to atmospheric H2S levels above the baseline concentrations. The results indicate that emissions from urban areas on the Mpumalanga Highveld, associated with sources in towns, as well as semi- and informal settlements (e.g. ineffective household combustion of low grade coal, sewage waste water treatment facilities, landfills, small industries and traffic) contributed most to atmospheric H2S levels in excess of baseline concentrations (34.6%), followed by pyrometallurgical smelters (19.8%) and a petrochemical operation near Secunda (17.9%). The Johannesburg-Pretoria megacity, coal-fired power stations, burning coal dumps and cattle feedlots contributed 10.9, 4.7, 3.8 and 0.4%, respectively, to H2S concentrations in excess of the baseline levels, respectively. The results from this study will be informative for legislation that is currently being considered, wherein regional ambient H2S standards for South Africa are suggested.