Hangzhou's first subway line will open later this year, with more already under construction.  The air quality was incredibly good - pure blue skies and clear sun for the days I was there.

You were spectacularly lucky.  Measured by PM10, Hangzhou's air quality is the third worst after Beijing (worst) and Nanjing (2nd worst).

When I last visited this past April 2012, here's what it looked like from the air:

http://flickr.com/gp/bruno-ken/97RM6f

And that was a sunny day:

http://flickr.com/gp/bruno-ken/17t93e

The top line of that "horizon" in the second picture is not in fact the land horizon, but rather the layer of polluted air sitting above the city, like a sea of toxic shit. Remarkably, the city itself is a green jewel of trees, leaves, bamboo and flowers, sprinkled by history, culture and mind-boggling concentrations of modern capitalist wealth.

What you wrote about Chengdu matched my experience almost exactly.  The locals quaintly call it "fog", as the Londoners used to in the 1950's.

Thanks very much for the diary, in particular the descriptions of Zhangjiajie National Forest Park and Fenghuang, both of which I will try to visit now.

Point n'est besoin d'espérer pour entreprendre, ni de réussir pour persévérer. - Charles le Téméraire