What is fog?

When the relative humidity reaches 100%, the water vapor in the air will condense into fine water droplets suspended in the air under the condition of sufficient water vapor, breeze and stable atmosphere, which will reduce the ground visibility. This weather phenomenon is called fog. Most of them appear between February and April in spring. Forming conditions: cooling, humidifying and increasing water vapor content. There are radiation fog, advection fog, mixed fog and evaporation fog.

Reason:

When the water vapor contained in the air reaches the maximum, it reaches saturation. The higher the air temperature, the more water vapor it contains. 1 m3 air, the maximum water vapor capacity is 6.36g at 4℃; When the temperature is 20℃, the maximum water vapor content in 1 m3 air is17.30g.

If the air contains more water vapor than saturated water vapor at a certain temperature, the excess water vapor will condense out. When enough water molecules combine with tiny dust particles in the air, the water molecules themselves will combine with each other and become small water droplets or ice crystals. The water vapor in the air exceeds saturation and condenses into water droplets, which is mainly caused by the temperature drop. This is why it is foggy in autumn and winter morning.