PM, abbreviation of particulate matter, PM10, particle size ≤ 10μm, PM2.5: particle size ≤ 2.5μm, they are the important components of the haze. Since the winter of 2013, PM2.5 has been in the public eye from time to time. It is in the dark and cannot be discerned by the naked eye, but it can precisely target us in the light, like a strong adhesive that adheres to our skin and upper respiratory tract, and waits for an opportunity to enter the human body and start a series of destructive works.