[W]hile Beijing's downtown API is 500 today, Yanqing is only 200.

according to the link you've posted above, an AQI value of 200 is considered "unhealthy."

though the use of the word "only" in the cited text was no doubt intended to contrast AQI levels in beijing and yanqing, the word is also subtly normative in the worst of ways.

i remember fearing (irrationally) for my life when i first moved to the capital in 1998 and the state-reported winter AQI values would top-out at 150-200 inside the 3rd ring road.

that was a long ten years ago in terms of china's development, to be sure. but it's also, now in retrospect, a scant few stumbles down the slippery slope of environmental degradation to a doubling or near-tripling of upper-marginal AQI values.

one wonders what AQI readings will prove news-worthy in yet another ten years' time.

good thing beijing isn't planning to host a winter olympics.

I believe that the scale tops out at 500 (I've seen it at exactly that value and no higher on a couple of occasions), so you really can't tell quite how horrendous it is! I love Beijing but it's a sick sick city.