I recall that our first speaker had shared with us a story about a woman who found out she had lung problems because she ran every morning in Beijing.
A new study shows that the level of PM2.5, the smallest solid particles in the atmosphere, is well above safe levels in most regions of China. Previous, Chinese government reported only PM10 (bigger particles) data, but due to rising public pressure it will start paying more attention to PM2.5. PM2.5 actually poses the greatest health risks and result from combustion activities (coal, wood, vehicles) as well as industrial activities.
The article has a map of China, color coded for different levels of PM2.5. Almost all of the regions surpass the level that is considered safe under the WHO guidelines (10mg/m^3)
and if you want to learn more about PM2.5 and PM10: