Nowadays,Enviromental protection has came a important subject in the world.There is an serious air pollution problem in the nothern of china which is called fog and haze.Fog and haze is an poisnous gas and it caused bad effects on people's body when they breath it in through their nose.
The question is what on earth decided whether or not the air is bad for us.PM2.5 is the scale of measurement of air quality.The air is harmful for our healthy when the value is more than 2.5 and is fine when the value is smaller than pm2.5.so,poeple are more and more pay attention to the PM2.5 and all realize the importance of pm2.5.