Beijing issued its first ever "Red Alert" due to the high levels of smog. This requires schools to close, construction work to stop, and cars are only allowed to drive on alternate days. The World Health Organization says that pollution over 25 micrograms per cubic meter is unsafe. Today's readings in Beijing reached 256 micrograms.
China burns a lot of coal for power, and also has a lot of construction projects. The dusts from the construction, the pollution from burning coal, and the car exhaust combine to form a dangerous blanket of smog.
Respirators for Smog Protection
You often see pictures of people wearing loose-fighting masks in high smog areas. These are mostly surgical masks, and do little to protect the wearer. These masks are designed to protect medical professionals from infection by limiting splashing and transmission of bodily fluids.
For smog protection, a tight-fitting respirator with an appropriate protection factor is required. The N95 disposable respirator is commonly used for this application, as it will filter out anywhere from 95% to 99.99% of particulates.