Organic and elemental carbon at a regional background site in South Africa

Atmospheric particulate matter (PM) contains a significant fraction of carbonaceous materials, which include organic- (OC) and elemental carbon (EC). These species significantly influence the global radiation balance and have negative health impacts. Although South Africa is an important emitter of carbonaceous aerosols, very little OC and EC studies have been published in the peer reviewed public domain. Therefore, the aim of this paper was augmenting the sparse OC and EC data for South Africa through a detailed assessment of an extensive dataset collected daily for 24 h over a period of 14 months at the regional background site, Welgegund. In total. 587 datasets were collected, which is the most comprehensive OC and EC dataset collected for this region. Seasonal OC and EC concentration patterns indicated significant contributions from open biomass burning in the months with highest fire frequencies, as well as contributions from household combustion during winter. In addition to these sources, the important influence of the industrial hub in the South African interior on OC and EC levels were also indicated. Meteorological conditions also contributed to increased OC and EC during the colder months. Since fire occurrences and population density decreased from east to west, OC and EC data associated with air masses mainly passing over eastern and western defined regions were compared. Although the differences were not as large as expected, statistical differences could be confirmed with air masses passing over the eastern region corresponding to higher OC and EC concentrations. Contextualization of OC and EC concentrations revealed OC and EC levels determined in this study were similar or slightly elevated compared to concentrations reported for other background sites. Furthermore, EC correlated well with equivalent black carbon (eBC), indicating that EC at this site can be used as a proxy for eBC at regional background sites.