How deadly is beijing's air pollution?

Not good: For most of the year Beijing has an air pollution index which would be unacceptable in the US. Chinese are willing to put up with it as a sign of progress and the fact that they are earning a living. There will be a burden of disease in the long run which will be tragic.

Air pollutants: It is a serious problem. When in Beijing smog/ air pollution can be a threat to your health. I found an excellent article on may ways to protect yourself. https://www.healthandsafetyinshanghai.com/china-smog/