The main thread for this is turning out to be in the China forum.
I have to ask: have you been to Shanghai or Beijing before? If you haven't, then you don't know REAL smog! There are times when staying in my hotel (where my room was on the 80th floor or so), I haven't been able to see the ground, solely due to the smog, and it is routine not to be able to see two blocks away.
Cloud cover occurs about 50% of the time mostly anywhere you go within the eclipse band within, say, 1000km of Shanghai, according to the NASA charts.