Why is it foggy in the morning?

In winter, due to the obvious ground radiation cooling at night, the "inversion layer" is easy to appear in the low altitude of the atmosphere, and the exchange and circulation ability of air in the horizontal and vertical directions becomes weak. The pollutants discharged into the air are confined in the shallow atmosphere and gradually gather into smog, leading to air pollution. At the same time, foggy days appear more frequently in winter. This is because the winter nights are long, there are more opportunities for sunny days and small winds, the ground heat dissipation is faster, and the temperature drop is more significant. When the temperature drops to the lowest in the morning, the water vapor in the air is easy to reach saturation and condense into small water droplets, which accumulate more and more and form fog.

From the meteorological point of view, when there is fog, it often means that the atmosphere is relatively stable, and the stable atmosphere is easy to accumulate pollutants, so foggy days are usually accompanied by mild or severe pollution. In many cases, low visibility weather is actually caused by the mixture of fog and haze. When the relative humidity is high in the morning, it is mostly fog, and it turns into haze after the temperature rises and the humidity drops during the day. Especially under the influence of heating, more pollutants are discharged in winter, which is also an important cause of winter smog.