Chinese Bureaucrats Argue Over Smog Causes

China's environmental ministry says winter heating is the cause (much of it coal powered). The ministry of urban development says it is car exhaust. The weather service says it is a weather related phenomenon.

Xinhua: 雾霾成因说法不该相互“打架”

My own take is that the main thing that changed for the worse in Beijing recently (past 5 years or so) is more cars, and that there is a real problem of inversion. Salt Lake City, which is a far, far less polluted city than Beijing (Salt Lake City triggers a yellow alert when PM2.5 hits 15 and a red alert at 25; Beijing PM2.5 is regularly over 100 on normal days and can climb over 1000 on the worst of days.)
It happens when warm air traps cold air below and significantly reduces air flow, causing pollution to build up:
Inversions occur during the winter months when normal atmospheric conditions (cool air above, warm air below) become inverted. Inversions trap a dense layer of cold air under a layer of warm air. The warm layer acts much like a lid, trapping pollutants in the cold air near the valley floor. The Wasatch Front valleys and their surrounding mountains act like a bowl, keeping this cold air in the valleys.

The worst thing about it is the government. The weather service can predict the inversion (they predicted one would begin this weekend and smog would peak around Tuesday), but the government doesn't preemptively limit pollution. It waits until the numbers are high and then triggers pollution reduction policies, which really don't help because the air doesn't clear until the weather changes. If they acted early, the situation might not get so bad in the first place.

But in any event, considering the situation in Salt Lake City, Beijing is going to have smog problems in winter for a very long time.

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