The correlation between pollution spike and temperature spike, if they are indeed linked, might be due to air-conditioners + non-insulated buildings ? The high temperature would push the air-con usage up, which would push the power usage up, pushing in turn the coal-fired energy plants. A way to confirm that would be a look at the hourly power usage of Suzhou's power plants... But I'm way too bad at Mandarin to get checking that :(

Hey doc, not sure if this contributes or not, but here goes. I and my girl drove to Anji last weekend, the mountains were beautiful as was the sky and water. When we were returning the farmers were burning their fields about an hour south west of Suzhou. The smoke was so thick you could barely breathe and visibility was down to about 50 meters.

The only thing that draws more attention to illegal fires and factory emissions than the stink would be the highly visible plume of smoke during the day.  So, they minimize their exposure by only burning/emitting at night.  They do it around here too.  I've seen burning brush piles that looked like they had more than a few tires thrown in for good measure.  With all the light pollution and smog, the night is never truly pitch black here, so the super black plume of smoke wasn't too hard to make out.

Shuzhou in Anhui province, which is a horrific shithole of pollution, or the one in Jiangsu province?

CharlieB and cooter are both spot on.

There are like 2 times per year that pollution gets really bad due to people burning down the country side. I've seen thousands of miles literally on fire while traveling by train.