The Department of Environment, Forestry and Fisheries (DEFF) say it is currently investigating the possible source of a sulphur stench experienced in parts of Gauteng and Mpumalanga.
This comes after widespread complaints of a sulphuric smell which has caused headaches and nausea.
The stench was most likely a combination of elevated levels of sulphur dioxide and hydrogen sulphide, the department said. However, at this stage the department said it cannot say definitively what the major source of the air pollution was.
During an inspection at Sasol’s Secunda Plant last week, the department said that it was found that the release of sulphur dioxide and hydrogen sulphide from the plant were within the approved limits of the Atmospheric Emission Licence (AEL) issued to it.
It added 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 2021, levels of hydrogen sulphide were found to have been elevated at times during the week in question.”
The deparment said that extreme peaks were noted at Lebohang monitoring station (234 parts per billion on the 12 February at 11h00) and Springs monitoring station (220 ppb on 16 February at 11h00).
“In Pretoria, hydrogen sulphide measurements at the South African Weather Service’s station in Irene, Centurion, showed that hydrogen sulphide exceeded the WHO recommendation on the 12th, 15th and until 17th February 2021, with the highest peak of 61 ppb on 16 February at 01h00).
“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.”
The World Health Organisation (WHO) recommends that hydrogen sulphide concentrations should not exceed 5.02 parts per billion (ppb) within a 30-minute averaging period in order to avoid substantial complaints about odour annoyance among the exposed population.
The department noted that 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 waste water works that also emit hydrogen sulphide. These include power plants and waste water works that also emit hydrogen sulphide.”
The department said that findings of the probe will be made available once completed.