Where does the smog come from?

Ok so this is my street on a beautiful blue-sky day: 

And this is the same street on a slightly worse than average day (but certainly not the worst!): 

The blue-sky days only happen once a fortnight, or once a week if I'm lucky!

I’ve been talking about the smog ever since I arrived here in Beijing, and I keep asking the question: where does it come from? Why do no other countries have such a dramatic problem?

I’ve finally found the answer in this article:

In January, a vice mayor of Beijing shared some figures for sources of Beijing air pollution. Of course, it is hard to independently verify these figures. But according to the local official, at least 22 per cent is from car emissions, 16.7 per cent from coal combustion, 16 per cent from building and road construction dust and particles, 6.3 per cent from industrial emissions, 4.5 from the burning of corn and wheat stocks and other activities in nearby rural areas. And 24.5 per cent of Beijing smog comes from surrounding urban and industrial areas, including Tianjin and Hebei. That’s what the vice mayor says, anyway.

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Many Western cities have gone through a very polluted stage. London used to suffer very badly from “London fog,” which was really smog. At first, people didn’t know the major source of air pollution was burning coal; then they realized it was a big problem, and London gradually phased out coal-fired power plants within city limits. That greatly reduced the discharge of sulphur dioxide, starting in the 1950s. Los Angeles faced a different type of air pollution — it was less about coal and more about car emissions. The way that L.A. addressed air-quality problems was by increasing mileage standards and fuel quality [in California], and also by improving the emissions-control devices installed on cars.

Air pollution in China is such a big challenge because it’s a combination of these two sources — coal combustion and cars. The newer coal-fired power plants do have stricter emissions standards, but meanwhile the number of cars is still rising quickly in Beijing and other cities. Beijing’s current plan does call for phasing out coal combustion within the Fifth Ring Road [an expressway encircling the city] and also retiring older, more polluting cars soon. But the surrounding areas outside of Beijing still have considerably less stringent standards on coal and car emissions, so this is a challenge.