What is the weather like at night?

The temperature of the ground drops slowly; By midnight, the ground temperature dropped even lower. At this time, it is in obvious contrast with the warmer temperature in the upper air. In this way, an inversion layer will appear above the ground. This "inversion layer" is like a big cover, covering the air, so that all kinds of dirty things in the ground air can not spread to the sky. In addition, plants spit out carbon dioxide at night, which also increases air pollution. Well, at six or seven in the morning, the air becomes the most stale. Also, "inversion layer" is most likely to appear in the evening. So the air at six or seven o'clock in the afternoon is also the most stale.