- Elevated levels of sulphur dioxide and hydrogen sulphide is believed to have caused the stench in Mpumalanga and Gauteng.
- Government has launched a probe into the cause of the stink.
- Findings of the probe will be made available once completed.
Government has promised to release the findings into its probe of the recent stink that hovered between Gauteng and Mpumalanga.
The stink is believed to have been a combination of elevated levels of sulphur dioxide and hydrogen sulphide.
Officials from the Department of Environment, Forestry and Fisheries (DEFF) and the Gert Sibande district municipality in Mpumalanga visited the Sasol Secunda Plant on 18 February.
They went to check on operations which were believed to be the possible source of the sulphur stench experienced in parts of the two provinces.
DEFF spokesperson Albi Modise said during their inspection, they found that the release of sulphur dioxide and hydrogen sulphide from the Sasol plant were within the approved limits of the Atmospheric Emission Licence (AEL) issued to them by the Gert Sibanda municipality on 23 April 2019.
DEFF and the municipality could not definitively reveal what the major source of the air pollution was.
"The DEFF and Gert Sibanda municipality suspect that the stench experienced over parts of Gauteng earlier this month may have been the result of the cumulative impact from a number of sources in the surrounding areas.
"While initial investigations have shown that the sulphur dioxide levels were in compliance with ambient air quality standards across all stations in the week of 11 to 17 February, levels of hydrogen sulphide were found to have been elevated at times during the week in question," Modise said.
Extreme peaks were noted at Lebohang and Springs monitoring stations.
In Pretoria, hydrogen sulphide measurements at the South African Weather Service's station in Irene, Centurion, showed that hydrogen sulphide exceeded the World Health Organisation recommendation on the 12, 15 and until 17 February, with the highest peak of 61 parts per billion (ppb) on 16 February at 01:00.
"The measurements show that there were two typical periods during the day when the levels of hydrogen sulphide were most severe, around 01:00 and 11:00 in the mornings. Such peaks are typical of transported air with pollution from high level sources such as tall stacks," Modise said.
Modise added that the WHO recommended that hydrogen sulphide concentrations should not exceed 5.02 ppb within a 30-minute averaging period in order to avoid substantial complaints about odour annoyance among the exposed population.
"There was also a low-pressure system in the north of the Mozambique Channel that gave rise to a rather uncommon circulation pattern over the region. These conditions created prevailing south-easterly winds that allowed for transportation of air pollution from the Mpumalanga industrial region into Gauteng, particularly over the cities of Ekurhuleni, Johannesburg and Pretoria.
"It has therefore been recommended that other sources that could have contributed to the odour experienced in the Gauteng also be investigated. These include power plants and wastewater works that also emit hydrogen sulphide. The findings of the probe will be made available once completed," said Modise.