Early morning smog hangs in the air as dawn breaks over Cape Town, August 3, 2003. A team of South African climatologists have begun a programme of research to establish the exact cause of the city\'s seasonal \"brown haze\", believed to be particularly bad this year, and monitor health effects. Picture taken August 3, 2003. REUTERS/Mike Hutchings Early morning smog hangs in the air as dawn breaks over Cape Town, August 3, 2003. A team of South African climatologists have begun a programme of research to establish the exact cause of the city\'s seasonal \"brown haze\", believed to be particularly bad this year, and monitor health effects. Picture taken August 3, 2003. REUTERS/Mike Hutchings
Aly Verbaan
RIVALRY between Durban and Cape Town has intensified over the years as they compete to become top sport, fashion or tourist attractions, but there is a more serious challenge facing the two cities – air quality.
To this end, Cape Town has 13 continuous ambient air quality monitoring stations that operate from fixed locations throughout the city.
Concentrations of all the pollutants measured are sent to the city’s Scientific Laboratory Services’ air quality laboratory every 10 minutes.
Each morning, statistical analyses are carried out on these ambient air concentrations, which are then compared against the national ambient air quality standards.
Mayoral committee member for health Siyabulela Mamkeli explained: “The analysers are extremely sensitive and can detect very low-level concentrations of pollutants, in the parts per million or microgram range. Even when no haze is evident, the low levels of pollutants present are recorded.”
The 13 monitoring stations are in Table View, Killarney, Potsdam, Bothasig, Goodwood, Foreshore, the CBD, Molteno, Athlone, Bellville South, Khayelitsha, Wallacedene and Somerset West.
“As is to be expected, the areas of the far south peninsula have the best air quality.
“This is because the region is supplied with clean air originating from the South Atlantic, and also because the most predominant wind direction in Cape Town is from a southerly direction,” said Mamkeli.
Townships are most often affected by localised pollution sources such as the burning of wood for fuel, cooking and space heating, he said.
The sheer number of braai stalls operating in informal settlements, as a source of income, can contribute quite significantly to poor ambient air quality, as seen in some of these areas.
“But by far the biggest source of air pollution in Cape Town is vehicular traffic, which makes up to 66 percent of the visible portion of air pollution,” he said.
“The brown discolouration in the haze is from the oxides of nitrogen (NOx) emitted by vehicle exhausts and other point sources.
“It has been found that brown haze episodes are linked to the temperature inversion conditions we experience in Cape Town over the May to September period.
“Cold air coming off the ocean is trapped close to the Earth’s surface overnight by a warmer layer above it. This warmer layer acts like a lid, preventing air pollution from dispersing (primarily from the morning traffic peak) until the cold air heats up through the course of the day by the action of sunlight.”
As Mamkeli explained, the National Air Quality Act specifies criteria pollutants that have to be monitored.
These criteria pollutants are not only pollutants in themselves, but also act as indicators of other pollutants in the air. The pollutants measured include sulphur dioxide (SO2), oxides of nitrogen (NOx), ozone (O3) and particulate matter (PM10 &2.5), carbon monoxide and benzene.
The location of the different analysers is determined by the area emission inventory, or the type of sources prevalent in a particular area due to a particular industry or activity that is found in the area.
The main purpose of the station is also important – does it serve as a regional (background) monitoring station, meso-scale or micro-scale, or transport-related station.
“The City Of Cape Town’s analysers continuously monitor these criteria pollutants every 10 to 15 seconds using state-of-the-art analysers that are maintained according to US EPA and SA Standards.”
While this sounds very proactive, the City of Cape Town Brown Haze Study report also attributed 65 percent of the visible pollution to vehicular emissions, of which 49 percent is caused by diesel-driven vehicle emissions.
In a business-as-usual scenario, air pollution is projected to increase by 48 percent over the next decade.
Worryingly, the World Health Organisation’s (WHO) most recent Cape Town air pollution survey (2013) states that the city “has the third-highest levels of air pollution in South Africa, putting residents at risk of getting sick and dying prematurely because of the growing level of outdoor air pollution”.
Predictably, Johannesburg and Pretoria score considerably worse than Cape Town, while Durban follows in fourth place. The WHO’s latest guidelines (2014) recommend a maximum limit of 10 micrograms per cubic metre for fine particular mass (PM) of 2.5 micrometres and no more than 20 µg/m3 for PM 10 (the measurement symbol for micrograms per cubic metre is µg/m3).
According to the report, PM10 levels in Cape Town were 30 µg/m3. Levels were more than three times higher in Johannesburg and about twice as high in Pretoria.
The May 2014 report stated that outdoor air pollution caused 3.7 million premature deaths worldwide in 2012, mainly from heart disease, strokes, chronic obstructive pulmonary disease, lung cancer and respiratory infections.
aly.verbaan@inl.co.za
