【2】Three main reasons for the formation of "Haze"

Shanghai in the haze

"Mist" and "haze", in fact, there are some differences between them. Fog refers to a kind of atmosphere, which visibility is less than 1 km due to the suspension of water vapor condensation and weather phenomenon; And the formation of gray haze mainly is caused by the joint action of a large number of suspended particles and meteorological condition. There are three main reasons for its formation：

-Calm wind increases in horizontal direction. Buildings in the city to build higher and higher, making the wind decreasing because of the block and less friction. This phenomenon goes against of the spread of aerosols in the atmosphere, so that they are easy to accumulate in urban areas.

- Temperature inversion appears in vertical direction. Thermal inversion layer is like a pot covering over the city. The temperature of high altitude is higher than low altitude’s, which restricting the air vertical motion of low altitude.  The suspended particles in the air hardly float to high altitude and stick in the low altitude.

- The increase of suspended particles in the air. As the growth of the urban population and industrial development, there is a great increase in pollutants and suspended solids, which directly leading to poor visibility.