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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 20 | Copyright
Atmos. Chem. Phys., 18, 15491-15514, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 29 Oct 2018

Research article | 29 Oct 2018

Seasonal influences on surface ozone variability in continental South Africa and implications for air quality

Tracey Leah Laban1, Pieter Gideon van Zyl1, Johan Paul Beukes1, Ville Vakkari2, Kerneels Jaars1, Nadine Borduas-Dedekind3, Miroslav Josipovic1, Anne Mee Thompson4, Markku Kulmala5, and Lauri Laakso2 Tracey Leah Laban et al.
  • 1Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
  • 2Finnish Meteorological Institute, Helsinki, Finland
  • 3Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland
  • 4NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 5Department of Physics, University of Helsinki, Helsinki, Finland

Abstract. Although elevated surface ozone (O3) concentrations are observed in many areas within southern Africa, few studies have investigated the regional atmospheric chemistry and dominant atmospheric processes driving surface O3 formation in this region. Therefore, an assessment of comprehensive continuous surface O3 measurements performed at four sites in continental South Africa was conducted. The regional O3 problem was evident, with O3 concentrations regularly exceeding the South African air quality standard limit, while O3 levels were higher compared to other background sites in the Southern Hemisphere. The temporal O3 patterns observed at the four sites resembled typical trends for O3 in continental South Africa, with O3 concentrations peaking in late winter and early spring. Increased O3 concentrations in winter were indicative of increased emissions of O3 precursors from household combustion and other low-level sources, while a spring maximum observed at all the sites was attributed to increased regional biomass burning. Source area maps of O3 and CO indicated significantly higher O3 and CO concentrations associated with air masses passing over a region with increased seasonal open biomass burning, which indicated CO associated with open biomass burning as a major source of O3 in continental South Africa. A strong correlation between O3 on CO was observed, while O3 levels remained relatively constant or decreased with increasing NOx, which supports a VOC-limited regime. The instantaneous production rate of O3 calculated at Welgegund indicated that  ∼ 40% of O3 production occurred in the VOC-limited regime. The relationship between O3 and precursor species suggests that continental South Africa can be considered VOC limited, which can be attributed to high anthropogenic emissions of NOx in the interior of South Africa. The study indicated that the most effective emission control strategy to reduce O3 levels in continental South Africa should be CO and VOC reduction, mainly associated with household combustion and regional open biomass burning.

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Short summary
Surface O3 was measured at four sites in the north-eastern interior of South Africa, which revealed that O3 is a regional problem in continental South Africa, with elevated O3 levels found at rural background and industrial sites. Increased O3 concentrations were associated with high CO levels predominantly related to regional biomass burning, while the O3 production regime was established to be predominantly VOC limited. Increased O3 is associated with strong seasonality of precursor sources.
Surface O3 was measured at four sites in the north-eastern interior of South Africa, which...