Recirculation of pollutants in the atmosphere of the South African Highveld

Atmospheric particulate concentrations were studied during a five-year period (1985-1990) at 23 sites on the South African Highveld. However, not all sites were operating concurrently or for equally long periods. Stacked filters (8 and 0.4 um) were exposed for 24 hours and then analysed for five species (sulphate, nitrate, chloride, phosphate and fluoride). More than 150 case studies have been selected from the five-year database, as well as from a subsequent one-year investigation at three sites. Synoptic features of the atmospheric circulation over the southern African subcontinent were linked with the behaviour of atmospheric particulates on the Highveld and categorized by a few classes of characteristic synoptic situations. Westerly ventilation, easterly ventilation and washout events were identified as being responsible for reducing sulphate concentrations over the Highveld on an average of 17 times per year.