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 (NO 2 ), sulphur dioxide (SO 2 ) and ozone (O 3 ), 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 NO 2 , SO 2 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. O 3 concentrations were found to be lower at sites with high levels of NO 2 , SO 2 and BTEX. NO 2 and SO 2 peaked during winter, while O 3 peaked in spring. NO 2 and SO 2 temporal concentration variations were ascribed to differences in seasonal meteorological conditions, as well as additional sources in winter. The O 3 peak coincided with a seasonal CO peak, which was identified as an important precursor for O 3 formation. No distinct seasonal trend was observed for BTEX. The annual average concentrations for SO 2 , NO 2 , O 3 and benzene were below the South African annual standards at all sites.

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Urban air pollution has become a major concern over the past decades. One of the largest conurbations in Sub-Saharan Africa is developed around the cities of Johannesburg and Pretoria (Jhb-Pta megacity). In this study, a photochemical box model with a detailed representation of ozone (O 3 ) formation chemistry was used to investigate the state of current air quality and photochemical processes in the Jhb-Pta megacity, as well as scenarios that could possibly mitigate air pollution. Results indicated that the Jhb-Pta megacity is within a VOC-limited (or NOx-saturated) regime. Major sources of NOx include transport from the Mpumalanga Highveld and local traffic emissions. O 3 levels in the Jhb-Pta megacity will be more effectively reduced if VOC (volatile organic compound) emissions are decreased. A reduction of NOx emissions leads to an increase in O 3 because of a decrease in titration through the reaction with NO. The same effect was observed in various cities worldwide where O 3 levels increased when NOx emissions were reduced during emission control strategies. The effect of reducing vehicular emissions in the Jhb-Pta megacity on the production of O 3 was also investigated. A significant increase of approximately 23 ppb O 3 was observed when emissions of VOCs, NOx and CO were reduced by changing from Euro-0 to Euro-3 vehicles. It is therefore recommended that VOC emissions are decreased together with the implementation of Euro-3 and cleaner vehicles in the future.