Global air quality readings fluctuate by the hour depending on human activity, the weather and the time of day.
Residents surveyed by environmental groups in Johannesburg have questioned the city’s air quality.
Breathe Cities and the Clear Air Fund (CAF) recently completed a poll of public perceptions that the municipality intends to use to formulate future policy.
However, global evaluation and ranking systems put Johannesburg well behind the world’s most dangerous cities for human respiratory systems.
AQI pollutants
International Air Quality Index (AQI) trackers measure the content of harmful air pollutants, with published figures given in real time being subject to weather and the movement of people through the city.
One of the key measurements is the concentration of particulate matter with a diameter of 2.5 micrometers or less, represented as PM2.5.
The AQI is given out of 500 based on the readings of multiple dangerous air pollutants, with any score over 150 considered unhealthy.
These pollutants measured include ground level ozone, nitrogen dioxide, carbon monoxide and sulphur dioxide.
Breathe Cities and CAF’s poll surveyed over 3 000 Johannesburg residents, with 92% stating that they were concerned about air pollution.
78% of those surveyed believed the air negatively impacted their health, but only 5% could point to any existing policies governing air quality.
“Demographic trends indicated the 30 to 35 age group exhibited the highest level of concern,” stated the city last week.
World’s worst air quality
Delhi was rated as the city with the most polluted air in 2024 with a daily average of 108.3 PM2.5 micrograms per cubic meter of air.
A microgram is equal to one-millionth of a gram, with the per cubic meter of air measurement expressed as µg/m3.
As of 11am on Monday, Johannesburg had a PM2.5 content of 25.5 µg/m3 , dropping to 16 µg/m3 by 1pm and an overall AQI of 64.
Simultaneously, Santiago in Chile had the second-worst air quality with 48.4 µg/m3 of PM2.5, 2.6 µg/m3 of sulphur dioxide and an AQI 137.
Above: The cities with the worst AQI as of 1pm on Monday.
Sulphur dioxide is emitted through industrial activity and vehicles, with Johannesburg’s Monday morning reading sitting at 9.3 µg/m3.
The African city with the worst air pollution is regularly Kinshasa, whose highest PM2.5 count and AQI over the last 30 days were 114.8 µg/m3 and 193, respectively.
Johannesburg’s highest PM2.5 count over the last 30 days was 38.9 µg/m3 on 12 June, which was accompanied by an AQI of 109.
Above: Johannesburg’s PM2.5 count over the last 30 days. Picture: IQAir.
‘Industrial activity and vehicles emissions’
Monday’s reading put Johannesburg 30th of the global rankings, which are subject to change on an hourly basis.
The survey in Johannesburg was split geographically, with residents in the southern suburbs noting high levels of waste burning.
Respondents in the northern suburbs listed industrial activity and vehicles emissions as their greatest concerns.
The municipality states that these insights will “directly inform” future residential engagements, policies, regulations, awareness campaigns and infrastructure investment.
“By investing in green infrastructure, clean energy, and public education, we can build a Johannesburg where clean air is a right, not a privilege,” said the city’s Director of Air Quality and Climate Lebo Molefe.
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