Industrial aerosol characterisation at a remote site in South Africa

South Africa is the most industrialised country in southern Africa with app roximately 1.1 Tg of sulphur emitted from anthropogenic activities per annu m. Complex circulation patterns and highly stable vertical atmospheric cond itions promote the accumulation of pollutants below 700 hPa or 3000 m asl. A remote site in the Eastern Cape of South Africa, Ben Macdhui (30.5 degree s S 27.9 degrees E, 3001m) was selected for testing the hypothesis that ind ustrial emissions, specifically sulphate, are transported over thousands of kilometres in anticyclonic type patterns of Bow and exported from the subc ontinent towards the Indian Ocean at about 30 degrees S. Time resolved part iculate sampling (streaker) was conducted between June 1995 and January 199 7. To characterise the industrial aerosol signal, two intensive sampling ca mpaigns (summer and winter) were undertaken in 1996. Aerosol samples were c ollected by a streaker sampler and an open-faced stacked filter unit (SFU). Samples were PIXE analysed to obtain elemental concentrations. The industr ial signature detected at Ben Macdhui was characterised by elevated concent ration of sulphur and iron in the fine fraction and fine sulphur detected i n the coarse mode. Other sources identified from the elemental data were so il (Al, Si, Ca. Rig, K. S, Mn), biomass burning (fine K) and marine (Cl, Ca , Mg, S and coarse K). These four sources accounted for approximately 70% o f the total detected elemental mass. Major individual contributions came fr om the crustal (53%) and industrial components (21%). Air parcel trajectory analyses confirmed that peak episodes of enhanced aerosol sulphur were rel ated to transport from the industrial Highveld region of South Africa and c onversely that clean air masses originated over the southern oceans. (C) 19 99 Published by Elsevier Science B.V. All rights reserved.