The normal range for PM2.5 is ≤2.5 microns. PM2.5 is also known as fine particulate matter, which refers to fine particles with a diameter of ≤2.5 microns present in the environment. The greater the concentration of PM2.5 detected in the air, the more serious the ambient air pollution. PM2.5 is smaller in diameter and more reactive than larger airborne particles, and it is very easy to adhere to various hazardous substances, such as microorganisms and heavy metals, etc. PM2.5 is not easy to be removed, and it remains in the air for a long time and spreads over a long distance, which is extremely harmful to the lives and health of residents. Residents living in industrially developed areas should pay attention to wearing a good mask to reduce the inhalation of PM2.5, and if you have respiratory discomfort, it is recommended that you seek medical treatment as soon as possible.