Concentrations, distributions and critical level exceedance assessment of SO2, NO2 and O3 in South Africa

Abstract

South Africa has been identified as a source of industrial pollution that is significant at a global scale. This study was designed to provide quantitative information, by direct measurement, across northeastern South Africa, which includes the highly industrialised Mpumalanga Highveld. The specific aim of the study was to evaluate whether or not acidic atmospheric pollution poses a threat to soils, plants and water bodies of South Africa. To address this aim, a network of 37 passive sampling sites was established to measure monthly mean concentrations of near-surface SO(2), NO(2) and ozone. The area covered extended over the northern and eastern interior of South Africa while avoiding sources of local emissions such as towns, mines and highways. The field campaign was conducted between August 2005 and September 2007. Spatial distributions and temporal trends for these pollutant gases were assessed. Critical levels analysis comparisons were made against applicable air quality standards, guidelines and limits to evaluate the potential for adverse atmospheric pollution impacts on regional environments. The assessment indicates that only in the central source area of the South African industrial Highveld are some levels exceeded. In remote areas, including the sensitive forested regions of the Drakensberg escarpment, pollutant concentrations are below the critical thresholds for environmental damage.

South African EUCAARI measurements: seasonal variation of trace gases and aerosol optical properties

“…It can be expected that higher tropospheric O 3 will occur further away from this source region, as the O 3 -precursors have more time to be converted to O 3 during the transportation. Martins et al (2007) and Josipovic et al (2010) reported much higher O 3 levels at background sites further away from the Highveld. The current South African ambient air quality standard for ozone is 61 ppb for an 8-h moving average, which is calculated from the 1-h moving averages (NEMA: AQA, 39 of 2004AQA, 39 of , 2009.…”

“…6, it is clear that regular exceedances of this standard occurred during the measurement period. Both the studies mentioned earlier (Martins et al, 2007;Josipovic et al, 2010) utilized passive sampling and could therefore not comment on exceedances of the 8-h moving average standard. However, considering that O 3 levels regularly exceeded this standard at the EUCAARI measurement site and that it is likely to be much higher as the plume from this source region is transported, it is evident that similar to e.g.…”

Atmospheric dry and wet deposition of sulphur and nitrogen species and assessment of critical loads of acidic deposition exceedance in South Africa

“…A database of ambient concentrations of acidic trace gas species SO 2 and NO 2 , measured at 37 remote sites across the region, was used. 28 Deposition velocities were obtained from an empirical set of dry deposition results measured in this region. 33 The wet deposition computation used prior long-term measurements of precipitation chemistry for the same region, 34 which were combined with precipitation measurements concurrent with the trace gas monitoring campaign.…”

“…20,21 However, unlike the modelled atmospheric concentrations used in the original study, the procedure adopted here used measured concentrations (gaseous and wet acidic anions). 28,34 Total (dry and wet) acid deposition loads were adjusted to account for mitigation as a result of base cation deposition. Soil sensitivity maps were generated, based on an empirical world soil database inventory.…”

“…Dry deposition values were based on measured ambient concentrations. 28 The second task was to assess any current exceedance of the critical sensitivity thresholds for soils where the soil buffering capacity to acidity is becoming saturated. The assessment was performed over a wider area, extending a few hundred kilometres upwind and downwind of the major point sources.…”