Air pressure, air density and humidity are closely related to altitude. Under the action of the earth's gravity, the air clings to the earth and forms atmospheric pressure. Under the action of the earth's gravity, air has a certain weight. The farther away from the earth's surface, that is, the higher the altitude, the lower the pressure, the smaller the air density, and the lower the humidity. In the range of 1 to 5 kilometers, the decline rate of air pressure is generally 10 kPa per kilometer.
The atmospheric pressure at the same altitude decreases with the increase of geographical latitude. With the increase of altitude, the pressure, air density and humidity are all decreasing.