The stench that drifted over parts of Gauteng on Wednesday is probably a combination of elevated levels of sulphur dioxide (SO2) and hydrogen sulphide (H2S), according to the department of forestry, fisheries and the environment (DFFE).
“There are many sources in the area as well as other provinces that could be contributing to these elevated levels,” said its spokesperson, Albi Modise. “From the ambient air quality monitoring observations on the South African Air Quality Information System, SO2 ambient levels, while elevated, have remained in compliance with ambient standards in Gauteng.”
SO2, a toxic gas, causes an odour even at concentrations far below those that cause health hazards. People sensitive to unpleasant odours may experience headaches and nausea. Exposure to high concentrations of H2S, a toxic gas with a characteristic rotten egg odour, can cause severe headaches and nausea.
The department, which is investigating the source of the pollution, was told that the stench was also detected in the North West.
“The department has noted concerns about the strong smell and is working with environmental and air quality officials in Mpumalanga, Gauteng, Limpopo and North West to determine the cause of the stench, and whether prevailing wind and weather conditions have contributed to the smell travelling over a long distance from another province, as was the case when a similar incident was reported in 2021,” it said.
Lauri Myllyvirta, lead analyst at the Centre for Research on Energy and Clean Air, said there was a spike in SO2 on Tuesday afternoon in Joburg, “which indicates that an industrial plume reached the city”.
“However, the measured level of SO2 is nowhere near the odour threshold, which is at least 1800ug/m3. So, it’s much more plausible that the plume was from a combined source of SO2 and H2S — that is, Sasol facilities. Wind direction was directly from Sasolburg,” he said.
In a blog in February last year, he said that Sasol is the largest emitter of H2S, which can be smelled at very low concentrations and there is no air quality monitoring for it in South Africa.
But Sasol spokesperson Matebello Motloung said it was not responsible for this week’s big stink. “Sasol can confirm that recently our Secunda and Sasolburg operations have been stable with no operational incidents that have/could have resulted in an increase in sulphur emissions. High resolution analysers, which monitor our emissions, report levels below the limits prescribed by our atmospheric emissions licences under which we operate.”
The Gauteng department of agriculture and rural development is “aware of the smell”, said its spokesperson, Nozipho Hlabangana. “The last time such an odour occurred was in 2021. The source was identified as having come from the Sasol plant located in Mpumalanga, following investigations by the DFFE. It is suspected that this might be a re-occurrence of the incident.”
He said the department will be liaising with the City of Johannesburg and the forestry, fisheries and the environment department in the investigation of possible sources. “The Gauteng air quality officers forum is also meeting this morning to investigate if there are no potential sources in the province.”
During the February 2021 sulphur stench that reached parts of Gauteng and Mpumalanga, Modise said it, too, was probably a combination of elevated levels of sulphur dioxide and hydrogen sulphide. An investigation into Sasol’s Secunda operations, which was believed to be the possible source, found that the release of SO2 and H2S from the plant were within the approved limits of its atmospheric emission licence.
Modise said on Thursday the result of its investigation into the possible source of that pollution had been “inconclusive”.