Fine particulates less than 2.5 micrometers across are recognised as hazardous to human populations.  The particles are so fine they cannot be easily expelled from the lungs. When the index value of these reaches between 300 to 500 then its is considered unsafe for everyone.  Below about 150 its unsafe for sensitive groups.  I took these shots one afternoon in Beijing when the rating was 400.

These pics show the effect of this pollution. You're not seeing mist or cloud here. That's fine particulates and emissions.

"Lost Skyline"
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"Above the Road"
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Shooting into the sun is usually not recommended. But I wanted a shot to show how much light the pollution was absorbing. And to emphasise the scene wasn't a product of shooting later in the evening.

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The colloquial term for the coughing that's endemic in Beijing is the "Beijing Ke"- literally, the Beijing cough.  It's often cured by leaving Beijing.
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"Situation normal" - this just seemed poignant at the time.
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I'm glad to be back in NZ. I only lasted an hour out there.