Atmospheric pressure is not fixed. In order to compare atmospheric pressure, at the 10th International Metrology Conference in 1954, scientists stipulated a "standard" for atmospheric pressure: at the sea level of latitude 45 and the temperature of 0℃, the pressure generated by a mercury column with a height of 760mm is called the standard atmospheric pressure. Its value is 10 1.325kPa, which is the unit of standard atmospheric pressure and is recorded as atm.

Extended data

Influencing factors:

1, the change of atmospheric pressure is related to altitude.

Atmospheric pressure is produced by gravity in the atmosphere. The higher the ground, the thinner the atmosphere, and the smaller the atmospheric pressure should be. However, because the air density related to the gravity received by the atmosphere varies unevenly with height, the atmospheric pressure decreases unevenly with height. Change with height: atmospheric pressure decreases with the increase of height.

The change of atmospheric pressure is also related to the weather.

At different times, the atmospheric pressure in the same place is not exactly the same. We know that the density of water vapor is less than that of air. When there is more water vapor in the air, the air density will become smaller and the atmospheric pressure will also decrease.

With climate change: Generally speaking, the air pressure is higher on sunny days than on cloudy days, higher in winter than in summer, and higher in morning than at noon. Often the atmospheric pressure decreases and the weather turns cloudy; When the atmospheric pressure rises, the weather will get better. There are many reasons for the change of air pressure, among which the change of temperature is a very important one.

When the air is cooled, the air contracts, the density increases, the weight of air column per unit area increases, and the air pressure also increases. So the arrival of cold air is always accompanied by the increase of air pressure, and when warm air comes, the air pressure will decrease again. Winter is a world of cold air and summer is a world of warm air, so obviously, the air pressure is high in winter and low in summer.

Baidu encyclopedia-standard atmospheric pressure