Why is Chongqing so foggy?

Chongqing, China is a famous foggy city, known as the "foggy city", with an average of 100 days of fog every year. When there is heavy fog, the visibility is sometimes only a few meters. Why is Chongqing so foggy?

It turns out that Chongqing is located at the confluence of the Yangtze River and its tributary Jialing River, with humid air and an annual relative humidity of over 80%. At the same time, Chongqing is surrounded by mountains, the ground is rugged, there is no strong wind blowing, and the water vapor in the air is difficult to spread. On a clear night, the ground heat radiation is intense and the temperature drops rapidly. The water vapor in the humid air near the ground condenses into countless tiny water droplets and floats at low altitude, thus forming fog. In winter, the sunshine time is short, the solar radiation is weak, and the fog cannot be completely dissipated during the day. After sunset, the dense cold air on the hillside will sink due to the influence of the terrain and accumulate at the bottom of the basin, making it easier to form fog.

This is the reason why Chongqing is foggy.