Since the City of Cape Town started a programme to test exhaust emissions of diesel-engine vehicles in 2000, there has been a dramatic decrease in the failure rate of diesel vehicles tested.

Exhaust emissions are responsible for the unsightly band of thick yellow smog – known as brown haze – that hangs over the False Bay coastline. Almost two-thirds of this pollution is caused by vehicle emissions, particularly diesel vehicles. Diesel emissions also contain carbon mixed with nitrate, sulphate, metals and other trace elements, all of which are bad for human health.

In 2000, 17% of vehicles tested failed the test; in 2008, 1.47% of vehicles tested failed the test.

According to David Oliver of the City’s Diesel Emissions Testing Unit,
the decrease can be attributed to the following factors:

• The decrease in the sulphur content in diesel from 5500ppm in 2000 to 3000ppm in 2003 and 500ppm in 2006
• Improved engine technology
• Visible policing
• Improved maintenance programmes by a number of major fleet owners
  

Air pollution officers randomly test diesel vehicles at various roadside testing sites, where drivers are asked to depress the accelerator of the vehicle, while the tester uses a light meter to measure the darkness of the smoke from the exhaust pipe. The driver of a vehicle failing these tests usually receives a spot fine of about R500. The owner must then repair the vehicle, and submit it for a retest within 30 days.

The most common causes of polluting exhaust smoke from diesel vehicles are wear and tear on the fuel pump; a faulty fuel injector; a clogged air filter; wear and tear of the engine block; soot and dirt deposited in the exhaust pipe, and worn piston rings.

Even though very few vehicles responded to the prosecution-free testing period, it is clear that the City’s Air Quality Management and diesel-testing programme is working, as the number of smoggy days every year have not increased as predicted.

The researchers of Cape Town’s Brown Haze 1 Report (1997) predicted that there would be a 45% increase in the number of brown haze episodes (the days on which pollution levels are above international standards) over 10 years if no action were taken by the City to control vehicular emissions. And although there are now more vehicles in Cape Town than there were 10 years ago, there has not been a resulting increase in brown haze, says Oliver.
To further reduce air pollution, in August 2005 the City of Cape Town adopted an Air Quality Management Plan (AQMP). The purpose of this plan is to ensure that clean air is achieved and maintained in Cape Town over the next 10 to 20 years. The AQMP contains the key objectives and strategies on which the City will focus to achieve its vision of Cape Town being the city with the cleanest air in Africa.

Other components of the programme include the revision of the City’s Air Pollution By-law. The proposed Draft Air Pollution By-law has been published for public comment. It aims to introduce stricter standards for smoke emissions from diesel vehicles and enhance compliance regarding industrial air pollution.