Analysis of trace gas emissions from spontaneous coal combustion at a South African colliery

Dlamini, Thabile Susan
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Atmospheric pollution resulting from an open-cast coal mine situated 10 km southwest of Witbank (Mpumalanga, South Africa) was investigated during summer and winter 2004. Industrial and urban activities in and around Witbank release large amounts of toxic and criteria pollutants into the atmosphere. Spontaneous combustion from the many collieries in the Witbank area contributes to this problem. Direct, automated, and continuous in situ measurements of trace gas concentrations and prevailing meteorological parameters were carried out by a mobile monitoring unit and an automatic weather station. The data collected show that spontaneous combustion is a source of CO, NO, SO2 and H2S. Summer daily averages of SO2, NO, NO2 and O3 concentrations ranged between 1 and 18 ppb, 0.3 and 40 ppb, 12 and 75 ppb and 0.9 and 19 ppb respectively. Winter daily concentrations of SO2 and O3 were much higher, ranging between 15 and 180 ppb and 14 and 30 ppb respectively. NO and NO2, in contrast, were lower in winter (0.8 to 15 ppb and 2 to 28 ppb for daily means). Winter daily average concentrations of H2S, CO and CO2 ranged between 16 and 217 ppb, 2100 and 5100 ppb and 322 and 436 ppm). Synoptic circulations over the Highveld were found to affect pollutant concentrations. During winter, temperature inversions played a significant role in increasing the pollutant concentrations in the early morning hours until about 10:00. Although considerable amounts of NO, NO2 and O3 were captured; their concentrations were within the South African Department of Environmental Affairs and Tourism’s permissible levels as contained in the National Environmental Management: Air Quality Act (2004). SO2 concentrations during winter 2004 exceeded the allowed standards. Elevated concentrations of pollutants were mostly observed when the wind blew from the SE, SSE, S and WSW directions, implicating the 2A south pits of the open-cast mine investigated as the major source of the emissions.
spontaneous coal combustion, coal combustion gas emissions, emissions open-cast coliery, weather impact on emissions