Why is there fog? What caused it?

Water in the air meets fog formed by condensation of cold air.

If the air near the ground is cooled to a certain extent, the water vapor in the air will condense into fine water droplets and be suspended in the air under the condition of sufficient water vapor, breeze and stable atmosphere.

It is foggy in autumn and winter morning, and the water vapor in the air exceeds saturation. During the day, the temperature of condensed water is higher, and the air can hold more water vapor. But at night, the temperature drops, and the ability to contain water vapor in the air drops, so some water vapor condenses into fog.

Especially in autumn and winter, due to the long nights, there are more opportunities without Feng Yun, and the ground heat dissipation is faster than that in summer, which leads to a sharp drop in the ground temperature, making it easy for the water vapor in the air near the ground to reach saturation in the middle of the night and condense into small water droplets to form fog.

Extended data:

The deterioration of visibility in foggy days is easy to cause traffic accidents. In highway traffic accidents, traffic accidents caused by bad weather such as dense fog account for about a quarter of the total, which not only hinders traffic, but also causes great losses to the country and people's lives and property.

Different shades of fog will cause visual errors, the driver's judgment of distance and speed is quite different from the actual situation, the visual distance is shortened, and it is easy to collide with the car in front. Especially on the expressway, once a traffic accident happens, it will often cause a chain reaction and eventually form a serious traffic accident.

The air pollution in foggy days is much more serious than usual. Another reason that needs to be emphasized is that the particles that make up the fog core are easy to be inhaled and stay in the human body, while the amount of air inhaled during exercise is much more than usual, and there will be a lot of particles inhaled during exercise in foggy days, further aggravating the harm of harmful substances to the human body.