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No new data shows South Africa’s Mpumalanga is world’s ‘worst nitrogen dioxide pollution hotspot’

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South Africa’s Mpumalanga province “is the worst nitrogen dioxide pollution hotspot in the world”. Melita Steele, Greenpeace Africa’s senior climate and energy campaign manager, made the claim in a prime-time TV interview in February 2019.

Steele was speaking on Carte Blanche, a weekly programme on pay channel M-Net. This pollution was caused by Eskom’s coal-fired stations in the area, which together accounted for “about 85%” of the country’s electricity, she said.

The Mpumalanga finding came from the international environmental group’s analysis of data from a new satellite captured in July and August 2018. Greenpeace released its analysis in October 2018.

In December 2018 Africa Check fact-checked the claim, and rated it misleading. This is because interviews with several scientists highlighted Greenpeace’s conclusion about nitrogen dioxide pollution had significant flaws.

Steele confirmed to Africa Check that her Carte Blanche interview was based on the same data.

It’s not disputed that Mpumalanga is a large source of air pollution. The fact has been well documented for years, including through satellite imagery, the experts told Africa Check. They agreed it was due to several large power stations operating near coal fields in the area.

Analysis done in South African winter

What was new was the level of detail in the satellite images used by Greenpeace, Prof Rebecca Garland told a parliamentary committee called in November 2018 to discuss the findings. She researches air quality and environmental health at the Council for Scientific and Industrial Research.

But the designation of Mpumalanga as the world’s largest air pollution hotspot was open to question for a number of reasons, the experts said.

This included the seasonality of Greenpeace’s data. The emissions period analysed by the organisation in 2018 was during South Africa’s winter.

In other parts of the world – such as eastern China, the eastern US and much of Europe – this emissions peak occurred in January, Garland said.

At least a year’s worth of data would be needed to draw such a conclusion, Garland later told Africa Check. Greenpeace was planning to do exactly this, Steele said on Carte Blanche.

Prof Pieter van Zyl of the School of Physical and Chemical Sciences at North-West University told Africa Check that ground-based measurements were also necessary to verify what was observed by satellites.  

Urban emissions sometimes higher

Further, Mpumalanga’s coalfields lie at a higher altitude, so its emissions were more visible to the satellite. To further cloud the findings, the international emissions inventories Greenpeace relied on did not capture localised sources of pollution well. This means that vehicle emissions, for example, were not as easily captured. It also has implications for how easy it is to compare different national data.

At certain times of the day nitrogen dioxide emissions over major South African urban areas, such as Johannesburg and Pretoria, were higher than those observed over Mpumalanga. This is according to a 2012 study by a team of researchers that included Van Zyl.

This was typically in the morning and early afternoon, when traffic is at a peak and most domestic burning occurs.

Nitrogen dioxide is produced by combustion, such as in car engines or when coal and gas are burned for energy.

The 25-kilometre radius Greenpeace used to define a “hotspot” was also an arbitrary measure and had no “scientific relevance”, Prof Harold Annegarn of North-West University’s School of Geo and Spatial Sciences said.

Air pollution in Mpumalanga is rightly of national concern, especially considering its effects on health. But the debate on improving air quality would richly benefit from accurate information. Greenpeace’s planned analysis of yearly data will be much anticipated. - Lee Mwiti (27/02/2019)


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