A strong sulphur-like smell, often described as resembling rotten eggs, has lingered across parts of Johannesburg for the past three days, leaving residents complaining about the unpleasant odour in the air.

According to the City of Johannesburg, the smell has been reported in several areas, including Sandton, Randburg, Roodepoort, and Fourways, with some complaints also coming from areas outside the city boundary.

Read more: Foul sulphide smell affects parts of Gauteng

The odour was first noticed on January 16, and was again reported on March 9, prompting the city’s environment and infrastructure services department to activate its air quality monitoring network to determine the source.

City manager Floyd Brink said technical teams immediately began monitoring air quality data following reports from residents. “Protecting the health and wellbeing of residents remains our priority. Our technical teams are actively monitoring air quality data and working with other spheres of government to determine the source of the odour and ensure residents are kept informed.”

Monitoring stations in Buccleuch and Alexandra detected elevated levels of hydrogen sulphide (H₂S), a gas commonly associated with the rotten egg smell. According to Tebogo Modiba, executive director of the city’s environment and infrastructure services department, hydrogen sulphide concentrations at the Alexandra monitoring station peaked at around 36–37 parts per billion, while sulphur dioxide reached approximately 52 parts per billion. “Technical monitoring confirmed measurable odour-related compounds during the episode.” He said, despite these short-term spikes, the city’s overall pollutant levels remained generally low and close to background levels, meaning that the concentrations recorded were high enough to produce a noticeable smell, but remain below levels typically associated with significant health risks.

Johannesburg is periodically affected by transboundary pollution, and the matter has been escalated to the department of forestry, fisheries, and the environment and the Gauteng department of environment to assist in identifying the source.

Also read: Councillor Mthembu explains the smell in Chartwell

Officials said the characteristics of the odour are consistent with emissions often linked to activities within the Highveld industrial complex.

Modiba said the city’s Air Quality Management Unit continues to analyse monitoring data and dispersion patterns, to better understand the origin and movement of the odour plume. “Residents are advised to remain indoors during periods of strong sulphur-like odours, and to avoid strenuous outdoor activity. Vulnerable groups, including the elderly, children, and individuals with respiratory conditions, should be monitored for symptoms such as eye or throat irritation, headaches, dizziness, or fatigue.”

According to the officials, Johannesburg does not host major heavy industrial operations, and all listed facilities in the city are licensed and regularly monitored by environmental inspectors.

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