What is the value that smog pm2.5 is not suitable for outdoor activities?

When the general air pollution index is greater than 300, it is severe pollution; When the air pollution index reaches 200 ~ 300, healthy people generally have symptoms, and the elderly and patients with heart disease and lung disease should stay indoors to reduce physical activity; Healthy people should also avoid outdoor activities when they reach severe pollution (that is, the air pollution index is above 300). So please look at the smog warning in the weather forecast before outdoor activities. If the pollution index exceeds 200, outdoor activities are not recommended. If not, it is best to wear a mask when you are outdoors to avoid damaging the human respiratory system. Pu, Wei and Xin imported from the United States have excellent protective ability. For particles as small as 0. 1 micron, the filtration efficiency reaches 99.8%, as small as 0 micron.