Clearing Beijing’s air pollution

The Asia Pacific Economic Cooperation (APEC) forum is just around the corner and a major clean-up operation is under way. Authorities are desperately trying to clear the air for the world leaders who will be descending on Beijing, but is there really anything that can be done?

Beijing’s air quality problems are not only due to the pollution it generates, but also a consequence of the geography of the region.

In the winter, there is often an area of high pressure over much of China. This pressure system effectively acts as a lid on the atmosphere, trapping any polluting particles close to the ground.

To the north and west of Beijing are huge towering mountains, and to the south and east are hundreds of other industrial cities which all generate their own high levels of pollution.

This means that if the winds are from the south or east, then they draw in the pollution from the surrounding cities. The mountains will prevent the pollution escaping northwestwards, and the area of high pressure will trap the smog at ground level in Beijing.

There are two types of weather which do help to clear the smog:

A wind from the northwest. This brings in clearer air, but the wind has to be reasonably strong in order for it to cross the mountains. Or rain. This effectively washes the polluting particles out of the air.

Credit for rain

In order to gain positive publicity, the Chinese government often claims credit for any rain that clears the pollution in Beijing, alleging that it uses a technique called ‘cloud seeding’.

Cloud seeding is a way of attempting to artificially generate rain, usually by firing particles of silver iodide into the air.

However, it is important to realise that the technique can only be successful if the conditions are conducive to rain. There must be a cloud there to begin with, and enough moisture to generate rain, otherwise cloud seeding will be useless.

In recent years, when the authorities in China have reported that they have successfully generated rain, the weather charts show that it would have rained in the city regardless of their efforts.

Pollution has long been a problem in Beijing, as it has in many other cities in China, and over the past few weeks, the pollution levels have regularly soared into the hazardous range.

If blue skies are to be seen for the forum, then not only do the industries in the region need to stop polluting the air, but the weather may have to lend a helping hand.