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

摘要

Atmospheric pollution resulting from an open-cast coal mine situated 10 km southwestudof Witbank (Mpumalanga, South Africa) was investigated during summer andudwinter 2004. Industrial and urban activities in and around Witbank release largeudamounts of toxic and criteria pollutants into the atmosphere. Spontaneous combustionudfrom the many collieries in the Witbank area contributes to this problem. Direct,udautomated, and continuous in situ measurements of trace gas concentrations andudprevailing meteorological parameters were carried out by a mobile monitoring unitudand an automatic weather station. The data collected show that spontaneousudcombustion is a source of CO, NO, SO2 and H2S. Summer daily averages of SO2,udNO, NO2 and O3 concentrations ranged between 1 and 18 ppb, 0.3 and 40 ppb, 12 andud75 ppb and 0.9 and 19 ppb respectively. Winter daily concentrations of SO2 and O3udwere much higher, ranging between 15 and 180 ppb and 14 and 30 ppb respectively.udNO and NO2, in contrast, were lower in winter (0.8 to 15 ppb and 2 to 28 ppb foruddaily means). Winter daily average concentrations of H2S, CO and CO2 rangedudbetween 16 and 217 ppb, 2100 and 5100 ppb and 322 and 436 ppm). Synopticudcirculations over the Highveld were found to affect pollutant concentrations. Duringudwinter, temperature inversions played a significant role in increasing the pollutantudconcentrations in the early morning hours until about 10:00. Although considerableudamounts of NO, NO2 and O3 were captured; their concentrations were within theudSouth African Department of Environmental Affairs and Tourism’s permissibleudlevels as contained in the National Environmental Management: Air Quality Actud(2004). SO2 concentrations during winter 2004 exceeded the allowed standards.udElevated concentrations of pollutants were mostly observed when the wind blew fromudthe SE, SSE, S and WSW directions, implicating the 2A south pits of the open-castudmine investigated as the major source of the emissions.