Andreas Späth

SA cities exceed WHO air quality limits

2016-05-16 11:32

Andreas Wilson-Späth

Cloudless winter mornings in Cape Town are gorgeous. From an elevated vantage point on the side of the mountain overlooking the Cape Flats, the sky is blue and the air crisp.

Then you notice the thin layer of smoky vapour that blankets the majestic panorama all the way to the Tygerberg Hills and the Hottentots Holland Mountains in the distance. If you hang around for a while, this layer of vaporous gunk starts to expand upwards as the cold night air that has been compressing it begins to dissipate and by mid-morning, you’re seeing the entire scene through a fog of brown haze.

That’s the air we breathe in our cities today. And it’s not good for us.

Air pollution is a major problem in most urban centres around the world. Smog in Chinese mega cities is legendary, but the problem is also prevalent in more surprising locations.

The scale of the crisis is evident in the World Health Organisation’s (WHO) latest urban air quality database. The organisation points out that “more than 80% of people living in urban areas that monitor air pollution are exposed to air quality levels that exceed WHO limits” and that “populations in low-income cities are the most impacted”. 

Almost all (98%) of cities with more than 100,000 inhabitants in low- and middle-income countries exceed WHO air quality limits, while just over half (56%) in high-income countries do so, too.

The database includes information for about 3000 cities in 103 countries. The quality of air is assessed by measuring the concentration of tiny particles (particulate matter or PM for short) of pollutants like black carbon, sulphate and nitrates it contains. PM10 refers to particles that are 10 micrometres (i.e. millionths of a metre) in size, while PM2.5 includes even smaller particles, a mere 2.5 micrometers and less in dimension.

Both types of particles can penetrate deeply into the lungs, but PM2.5 particles are generally more dangerous than PM10 particles. Potential health effects include a significantly increased risk of heart disease, lung cancer, stroke, as well as chronic and acute respiratory illnesses, including asthma. These measurements do not account for other hazardous, gaseous pollutants such as ozone and nitrous oxide.

The WHO recommends that annual mean concentrations of PM2.5 and PM10 should not exceed 10 and 20 micrograms per square metre, respectively.

So which cities have the world’s most polluted air?

China has managed to improve some of its notorious urban air pollution problems and now has ‘only’ 5 representatives in the list of the top 30 most polluted cities when it comes to PM2.5. With 16, India has the most.

The two cities with the most foul air on the planet, however, are elsewhere.

Onitsha, a rapidly growing Nigerian port city on the Niger River, has the dubious distinction of having the highest mean annual PM10 reading in the WHO database: 594 micrograms per square metre – a staggering 30 times the recommended level.

The city with the highest mean annual PM2.5 measurement (217 micrograms per square metre) is Zabol in Iran.

What about South African cities?

The WHO database for South Africa (and the rest of the continent) is unfortunately rather limited. It lists 13 locations, but excludes major centres like Cape Town, Durban, Port Elizabeth and Bloemfontein. Most of the annual mean PM2.5 and PM10 values date to 2014 (with a few from 2013 and 2011).

The numbers, although nowhere near as dire as in some other parts of the world, are not great.

For both PM2.5 and PM10, the annual means for all 13 South African sites fall above the WHO guidelines (in the majority of cases, the annual mean values are, in fact, higher than the recommended 24-hour mean concentrations as well).

The worst annual mean concentrations of the 13 South African sites are:

PM10: 119 micrograms per square metre (5.95 times the WHO guideline)
PM2.5: 60 micrograms per square metre (6 times the WHO guideline)

PM10: 85 micrograms per square metre (4.25 times the WHO guideline)
PM2.5: 41 micrograms per square metre (4.1 times the WHO guideline)

Tshwane (Pretoria)
PM10: 63 micrograms per square metre (3.15 times the WHO guideline)
PM2.5: 51 micrograms per square metre (5.1 times the WHO guideline)

Think about all of that the next time you take a breath.

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath

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