Time to clear the air
February 10 2013 03:08 AM


 Rush hour traffic heads west, fading into the smog at dusk on the North Third Ring Road in Beijing, China, in this archive picture. The dry and calm conditions that are seen for long stretches during the Asian winter are the ideal conditions for smog to form.


Both Beijing and Delhi, vast industrialised cities, are

suffering due to smog caused by pollution. By Steff Gaulter


If you’ve been watching the news recently, you’ll have seen the unpleasant images from the large Asian cities of Beijing and New Delhi. Both of these vast cities, home to a total of over 35mn people, have been shrouded in dense clouds of toxic smog.

In Beijing, the pollution on some January days was so bad that people were advised not to go outside. Visibility in both cities reduced to less than 100m, leading to flight cancellations and numerous traffic accidents. In a desperate attempt to alleviate the problems, the governments brought in strict emergency measures, including shutting factories and restricting the number of cars on the roads.

Clearly both cities are vast industrious metropolises, each of which pour vast quantities of pollution into the atmosphere every single day, but something seems to have happened to make the pollution worse than usual.

Particles that cause pollution can come in any shape or size, and they are usually classed according to their dimension. The larger ones are called PM10 (particulate matter up to 10 microns in size) and the smaller ones are PM2.5 (particulate matter less than 2.5 microns). Both are very small, but the smaller ones, the PM2.5 particles, are 100 times smaller than the width of a human hair. This is clearly incredibly tiny, but these finer particles are actually the ones that are more damaging to your health.

PM10 particles are made up of smoke and dirt from factories and farming, as well as from tiny pieces of rocks and plant spores. They are generally created by grinding rocks or turning soil, and the particles are then blown by wind. PM2.5 particles, on the other hand, are toxic organic compounds and heavy metals. These finer particles are generated by the exhaust of vehicles, the burning of plants or by metal processing plants.

Clearly looking at the list of things that generate the different particles, it is fairly obvious that PM2.5 particles consist of substances which are more toxic, but this isn’t the only reason that they are more dangerous. Whereas bigger particles are more likely to get stuck to the sides of the lungs, the smaller PM2.5 particles can penetrate further. If the toxins become embedded in your lungs, they can cause various lung diseases.

Unfortunately as well as being more hazardous, these finer particles can also spend longer suspended in the atmosphere. The larger ones will tend to settle out of the air after just a few hours, but the PM2.5 particles can travel for hundreds of miles and can stay in the air for days or even weeks. Recently it has been these tiny PM2.5 particles which have caused such great concern in Beijing and New Delhi.

The World Health Organisation (WHO) has an air quality index for PM2.5 particles. Levels below 15 micrograms per cubic metre are classed as ‘good’. Above 40 micrograms per cubic metre, the level is said to be unhealthy for those people who are sensitive to their surroundings, including asthma sufferers. The scale continues to get worse, with the most severe category being between 250 and 500 micrograms per cubic metre. The pollution in Beijing on 12 January was so severe that it was completely off the scale, reaching the unenviable levels of 993 micrograms per cubic metre. The number of people admitted to hospital with respiratory problems increased by 20%.

A few weeks later, on January 31, it was reported that in India, the pollution in New Delhi was ‘worse than Beijing’. While this may have been true on this particular day, it wasn’t worse than Beijing had been at its peak, 9 days earlier. With a reading of 400 micrograms per cubic metre, the air in New Delhi was clearly hazardous, but at least it was still on the scale.

New Delhi and Beijing are not isolated cases. Many other cities in mainland Asia have also suffered from severe smog conditions recently and it’s no coincidence that this has happened at this time of year. During the winter, the huge Eurasian landmass gets very cold. Cold air is dense and heavy, so as the temperatures drop, the heavy air starts to push down on the earth. This causes the pressure to rise, and a large area of high pressure forms over the landmass. The sinking air acts as a lid on the atmosphere, and the pollution is all trapped near the ground, unable to escape.

Regions of high pressure also normally bring periods of dry, still weather. This again works to makes the air quality worse. A proper downpour will wash the pollution out of the atmosphere, and a strong wind would disperse the particles. However, with dry, settled weather the pollution which is created in the cities doesn’t clear. The fine particles hang in the air, whilst yet more pollution is created. The smog just continues to get worse.

The dry and calm conditions that are seen for long stretches during the Asian winter are the ideal conditions for smog to form. The only real way for Beijing and New Delhi to clean up their air permanently is to reduce the pollution that they generate. In both cities, proposals are being drafted in an attempt to improve the air quality. The ideas include stricter regulations for builders, annual inspections of the emissions of private vehicles and higher parking fees in an attempt to persuade people to use public transport.

Without action, these cities could find they have the same problem which London faced in the 1950s. At the time the city was famous for its thick smogs, which were known as “peasoupers”. The worst outbreak occurred in 1952, when more than 4,000 people died after the city was engulfed in a toxic blanket of smog for just five days. This number of deaths in such a short period of time clearly indication of how seriously the subject of air quality should be taken. However, it also shows that with the right legislation, these problems can be overcome.



(The author is Senior Weather Presenter at Al Jazeera English channel. She can be contacted on [email protected]
or on Twitter at @WeatherSteff)


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