Detection of non-sea salt sulphate aerosol at a remote coastal site in South Africa: A PIXE study

An aerosol sampling site based on a single-stage streaker sampler with four -hour time resolution was established in 1993 at Brandt-se-Baai, on the nor th-western coast of South Africa (31.5 degrees S 18 degrees E, 50 m asl). T he site was deployed to monitor the generation of just from the local minin g operations and in part to test the hypothesis of large-scale air mass rec irculation over Southern Africa. Streaker samples were analysed by PINE for the usual crustal derived elements and sulphur. Sulphate aerosols over sou thern Africa are produced in the atmosphere by oxidation of SO2, from indus try, or DMS, from the ocean. Industrial related sulphate Flays a key role i n tracing long-range transport of anthropogenic pollutants. We present results from selected monthly samples collected during 1996, Mea sured ecl particulate sulphur has been apportioned between contributions fr om sea spray and non-sea salt sulphate (NSS) aerosols. Marine particulate s ulphur, present in the regional background. was traced by its correlation w ith Na and Cl, which were routinely detected, The NSS content of these air masses was enriched with respect to the expected sea salt sulphur by two or ders of magnitude. Al, Si, K;, Ca, Ti and Fe, the major crustal elements, w ere measured only episodically with the occurrence of strong south-easterly winds. These u inds are associated with wind blown dust from a mine locate d 4 km from the site. These results are the first direct aerosol characterisation of the remote r egion of the western seaboard of southern Africa. Specifically the sulphur measurements at this site provide insights into relative contributions of n atural DMS. industrial and sea salt contributions of particulate sulphate. (C) 1999 Elsevier Science B.V. All rights reserved.