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

Laban, Tracey Leah; van Zyl, Pieter Gideon; Beukes, Johan Paul; Vakkari, Ville; Jaars, Kerneels; Borduas-Dedekind, Nadine; Josipovic, Miroslav; Thompson, Anne Mee; Kulmala, Markku; Laakso, Lauri

Although elevated surface ozone (inline-formulaO3) concentrations are observed in many areas within southern Africa, few studies have investigated the regional atmospheric chemistry and dominant atmospheric processes driving surface inline-formulaO3 formation in this region. Therefore, an assessment of comprehensive continuous surface inline-formulaO3 measurements performed at four sites in continental South Africa was conducted. The regional inline-formulaO3 problem was evident, with inline-formulaO3 concentrations regularly exceeding the South African air quality standard limit, while inline-formulaO3 levels were higher compared to other background sites in the Southern Hemisphere. The temporal inline-formulaO3 patterns observed at the four sites resembled typical trends for inline-formulaO3 in continental South Africa, with inline-formulaO3 concentrations peaking in late winter and early spring. Increased inline-formulaO3 concentrations in winter were indicative of increased emissions of inline-formulaO3 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 inline-formulaO3 and CO indicated significantly higher inline-formulaO3 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 inline-formulaO3 in continental South Africa. A strong correlation between inline-formulaO3 on CO was observed, while inline-formulaO3 levels remained relatively constant or decreased with increasing inline-formulaNOx, which supports a VOC-limited regime. The instantaneous production rate of inline-formulaO3 calculated at Welgegund indicated that inline-formula∼40 % of inline-formulaO3 production occurred in the VOC-limited regime. The relationship between inline-formulaO3 and precursor species suggests that continental South Africa can be considered VOC limited, which can be attributed to high anthropogenic emissions of inline-formulaNOx in the interior of South Africa. The study indicated that the most effective emission control strategy to reduce inline-formulaO3 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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Laban, Tracey Leah / van Zyl, Pieter Gideon / Beukes, Johan Paul / et al: Seasonal influences on surface ozone variability in continental South Africa and implications for air quality. 2018. Copernicus Publications.

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