[tim333]

Apparently it was taken Saturday 12 Jan 2013 'when the PM2.5 reading reached 886 micrograms per cubic metre, according to the [US] embassy's "BeijingAir" Twitter feed.'

http://www.scmp.com/news/china/article/1127398/smog-threat-r...

(date taken from the wsj thing http://blogs.wsj.com/photojournal/2013/01/14/photos-of-the-d...)