Spatial and temporal assessment of gaseous pollutants in the Highveld of South Africa

Abstract

Diverse natural and anthropogenic activities in the Highveld of South Africa contribute to elevated levels of inorganic and organic gaseous pollutant species. The primary aims of this investigation were to determine spatial and temporal distributions of nitrogen dioxide (NO₂), sulphur dioxide (SO₂) and ozone (O₃), as well as benzene, toluene, ethylbenzene and xylene (BTEX) in this area. Sampling was conducted on a monthly basis for a year at eight strategically selected sites. The highest NO₂, SO₂ and BTEX concentrations were measured at sites with significant local sources and/or sites impacted by more remote sources, as indicated by overlay back trajectories. O₃ concentrations were found to be lower at sites with high levels of NO₂, SO₂ and BTEX. NO₂ and SO₂ peaked during winter, while O₃ peaked in spring. NO₂ and SO₂ temporal concentration variations were ascribed to differences in seasonal meteorological conditions, as well as additional sources in winter. The O₃ peak coincided with a seasonal CO peak, which was identified as an important precursor for O₃ formation. No distinct seasonal trend was observed for BTEX. The annual average concentrations for SO₂, NO₂, O₃ and benzene were below the South African annual standards at all sites.