Go to Home Depot, buy a few "N95 Approved" dust masks. My favorite for when I'm there is a 3M 8511.
.... Seriously, you should do it. Smog in Beijing is awful in Jan. Go to AQICN.COM. Smog in Los Angeles is around 70 to 130 on a bad day, in Beijing, it's off the international scale at 500+.
Just sayin,
FR