Temperature : When the temperature of a place increases, the atmospheric pressure decreases. This happens because an increase in the temperature results in the heating of the air. Warm air expands. The molecules of the warm air become less dense and hence exert less pressure. On the contrary, decrease in temperature makes the air cool and dense. This creates a high pressure area in a region.
Altitude : Atmospheric pressure decreases with an increase in the altitude. Air is compressible. As the gravity of the Earth pulls the molecules and gases towards the ground, the lowest layer of the air becomes densest. This dense layer of air exerts the greatest pressure.
Rotation of the Earth : The rotation of the Earth causes the air at the Poles to be pushed away towards the Equator. In theory, air should have been accumulated at Equator creating a high pressure belt. However, this does not happen. On the contrary, the air gets heated at the Equator, and rises up creating a low pressure.