Attitude, Temperature and humidity are the various factors that effects atmospheric pressure.
Attitude :- When height increases pressure decreases when height increases the amount of air present in atmosphere decreases.
Temperature :- When air gets heated, air starts to expend. As a result air become dense and it rises. This leads to decrease in pressure.
Humidity:- The amount of water vapour present in air is called humidity. The water vapour is less dense than air. So when the amount of water vapour increases atmospheric pressure decreases.