Abstract
We tested the hypothesis that acidic atmospheric pollution deposition, originating from the South African central industrial area, poses an environmental threat across a larger region within the dispersal footprint. A network of 37 passive monitoring sites to measure SO2 and NO2 was operated from August 2005 to September 2007. The area extended over the entire northern and eastern interior of South Africa. Monitoring locations were chosen to avoid direct impacts from local sources such as towns, mines and highways. Dry deposition rates of SO2 and NO2 were calculated from the measured concentrations. Concentrations of sulphur and nitrogen species in wet deposition from a previous study were used in conjunction with measured rainfall for the years 2006 and 2007 to estimate the wet deposition over the region. The calculated total (non-organic) acidic deposition formed the basis for an assessment of exceedance of critical loads based on sensitivity of the regional soils. Regional soil sensitivity was determined by combining two major soil attributes available in the World Inventory of Soil Emission Potentials (International Soil Reference and Information Centre). Results indicate that certain parts of the central pollution source area on the South African Highveld have the potential for critical load exceedance, while limited areas downwind show lower levels of exceedance. Areas upwind and remote areas up and downwind, including forested areas of the Drakensberg escarpment, do not show any exceedance of the critical loads.
Highlights
A large proportion of this industrial infrastructure is concentrated on the Highveld plateau, which accounts for approximately 90% of South Africa’s scheduled emissions of industrial dust, sulphur dioxide (SO2) and nitrogen oxides (NOx).[6]
Total deposition estimates were highest for the site with high dry deposition and relatively high wet deposition
This study investigated the risk of acidification from both sulphur and nitrogen non-organic acidifying species, anthropogenic and natural, through the method of critical loads mapping
Summary
Terrestrial acidification as a result of atmospheric pollution continues to be an environmental problem of concern for developing countries, in light of increasing emissions of acidic precursor trace gases.[1,2,3] South Africa has one of the largest industrialised economies in the Southern Hemisphere and is the only industrialised regional energy producer on the African continent.[4,5] A large proportion of this industrial infrastructure is concentrated on the Highveld plateau, which accounts for approximately 90% of South Africa’s scheduled emissions of industrial dust, sulphur dioxide (SO2) and nitrogen oxides (NOx).[6] There are three pathways by which chemical species can be removed from the atmosphere: chemical transformation, wet deposition and dry deposition. The central task of this study was to derive combined dry and wet deposition of acidic trace gases, and to assess exceedances of critical sensitivity thresholds, taking into account soil properties and base cation deposition.
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