Atmospheric pressure is influenced by various factors. Most important among them are:

a. Temperature: There is a close relationship between temperature and pressure conditions of the air. Higher the temperature, lower will be the pressure and vice-versa. When the air is heated, the molecules expand and the air becomes light. The tropical region receives almost perpendicular rays of the sun. As a result, the air is heated and raised upwards in the form of convectional currents and has become a low pressure belt. 

b. Altitude: The air pressure is associated with altitude or height. Much of the atmospheric air is concentrated in the lower layers of the atmosphere. With the increase of height pressure decreases but not always at constant level. On the basis of this principle “Altimeter’ is invented. This instrument measures the pressure of Atmosphere and denotes corresponding height of the place from the mean sea level, 

c. Water Vapor: The amount of water vapour in the air also influence on the atmospheric pressure. Water vapour is lighter than air. So more the vapour lighter will be the air. The dry air is heavier than vapour laden. It is because of this reason the air with more amount of vapour becomes lighter and raised upwards leading to condensation and precipitation.

d. Rotation of the Earth: The spinning of the earth on. its axis also causes variation in the atmospheric pressure. The spinning action also causes spinning of air mass and the cold air near the poles is rarefred to form low pressure belts.