Air pollution is the accumulation of various substances such as dust, gas, mist, odour, and smoke in the ambient air. These substances contain pollutants such as SO₂, NO₂, CO, H₂S, O3, PM-10 and VOCs (volatile organic carbons). These pollutants have been identified as “priority” or “criteria” pollutants in the National Environmental Management: Air Quality Act, 39 of 2004 (AQA) and the City of Cape Town’s Air Quality Management Plan (2005).

The National Environmental Management: Air Quality Act, 39 of 2004 defines the limit values for criteria pollutants. These are known as the South African National Standards for ambient air quality. When pollutants exceed set limits, it could have adverse impacts on our health and well-being as well as plant and animal life and the environment.

Measuring and monitoring the quality of the air we breathe is important to:

• provide a scientific basis for management and control of air pollution
  
• determine if air quality health standards are met
  
• provide the public with measurements on air quality
  
  

The information below covers the following: 

• Where and how air pollution is measured?
• The quality of air in the city
• Data analysis and evaluation
• Long term trends
• Climate change
  
  

Where and how is air pollution measured?

The Air Quality Laboratory of Scientific Services Branch is responsible for measuring and monitoring the air quality in the City of Cape Town.

During the 1960s the occurrence of “Black Smog”, mainly as a result of pollution from coal and oil burning sources, necessitated the setting up of a number of monitoring stations to determine concentrations of Sulphur Dioxide (SO₂) and black smoke. In the early 1970s automated equipment was used to monitor the air. In 1984, state of the art analysers that continuously monitor the air were installed. Since then, the City’s Air Quality Monitoring (AQM) network has evolved and has expanded to twelve stationary sites and one mobile site. 

Click here to view a map showing the location of the monitoring sites.

Air pollution instruments are housed in caravans called monitoring stations. A monitoring station can be thought of as a self-contained field laboratory.

Air is continuously drawn from outside the station and is sampled by the instruments. Sulphur dioxide (SO₂), oxides of nitrogen (NOx), ozone (O3), carbon monoxide (CO), hydrogen sulphide (H₂S) and particulate matter (PM 10) is measured every 10 seconds using US EPA approved methods. At each site, the data is stored on a Data Acquisition System. This DAS system is responsible for storing, pre-validation and transmitting this data onto the AQM Network.


The AQM Laboratory of Scientific Services is responsible for the installation, repairs, maintenance and calibration of these sophisticated analysers by following strict ISO 17025 standards. The laboratory has been SANAS accredited since 2006 for the SANS ISO 17025 accreditation system.

The quality of air in Cape Town

The quality of the city’s air is significantly affected by meteorological conditions such as wind, cloud cover, rain and temperature.

Under stable atmospheric conditions with low-level temperature inversions, a visible brown haze hangs over the city, spoiling exciting vistas of mountain ranges and sea views. This haze occurs mainly during March to September, but of recent has extended into the summer months as well.

Sources of the pollution in Cape Town are emissions from transport (road, rail and sea), industrial processes, waste disposal, wild fires and fuel burning from domestic heating.

Pollutants may be referred to as primary or secondary.

• Primary pollutants are emitted directly into the atmosphere from identified sources such as transportation, industrial processes, fuel or solid waste disposal and tend to be highest around the sources, e.g. SO₂, NOx, CO, H₂S, PM-10
  
  

• Secondary pollutants are formed by chemical reactions in the atmosphere among the primary pollutants. They are strongly influenced by meteorology and atmospheric chemistry, e.g. O3, PM-10, NO₂

Data analysis and evaluation

The AQM Network is managed by a specialised AQM System (AQMS).  Data is transmitted to the Air Quality Monitoring Server hosed at Scientific Services via internet communication. The AQMS Database is available to users for further processing, analysis and reporting.

Statistical analysis and reporting systems are used to validate and evaluate data and assess if the pollutants are within set guideline limits.

The City of Cape Town has adopted the UK guideline limits in its State of Environment Report but also assesses air quality data against the South African National Standards. Episodes occur when any of these limits or standards are exceeded.


Monthly reports and special reports are generated for clients and the public. Information provided includes hourly, daily and monthly concentrations, what pollutants are exceeded, where they have been exceeded, concentration value of exceedences compared to guidelines, when and duration of events and possible sources.

The information is reported here, and is mainly used by the City’s Health Department to enforce legislative requirements and to manage and control air pollution.

Long term trends

Concentrations of air pollutants in the atmosphere can vary over the course of a day, the seasons of the year and from year to year.

Seasonal variations show certain pollutant peaks during winter e.g. PM-10 and CO, while other pollutants peak in summer e.g. O3 peaks in summer. The total number of days per annum that Cape Town experiences pollution episodes is assessed for annual trends. The annual trend indicates that overall levels of air pollution are decreasing although the nature of air pollution events are more severe and often fall into the “Top10” category of the highest concentrations of pollutant levels monitored in the last ten years.



Monthly trends show that winter has the highest occurrence of episodes.

The information from the AQM Network feeds into the City’s “Air Quality Management Plan”.
The City aims to “be the city with the cleanest air in Africa”. Short, medium and long term strategies for improving air quality over the entire region have been identified and are currently being addressed. One of the City’s primary objectives is to reduce the health effects of poor air quality on residents, especially during Brown Haze episodes.

Climate change

It is predicted that Cape Town will face some degree of climate change in the 2030 to 2045 period.

A number of stress factors have been identified in this regard:

• Increase in annual average temperature (1°C by 2050 & between 3°C - 5 °C by 2100)
  
• Increase in frequency & intensity of extreme events
  
• Increase in conditions conducive to wildfires (higher temperatures & increased wind velocity)
  
• Reduced rainfall
  
• Decrease in water resources
  
• Reduced soil moisture
  
• Temperature impact on crop activities
  
  

The two key ways to respond to climate change is through:

• Mitigation (the reduction of the intensity of climate change effects by reducing greenhouse gases)
  
• Adaption (recognising the effects of climate change and adapting to these changed conditions)
  
  

The AQM Laboratory has responded to climate change by providing input on various climate change working documents and establish linkages between the projects undertaken in various departments and the role of Scientific Services.

Analysis of air quality data related to climate change can be used to inform the planning and implementation of various interventions. The AQM Laboratory is developing a monitoring and evaluation strategy for the monitoring of climate change impacts.