When temperature increases air gets heated and expands. The expanded air is less dense and it ascends. This leads to lowering of pressure. When temperature decreases, air becomes dense and descends.
This will increase atmospheric pressure. So there is an inverse relationship between temperature and pres sure. When altitude increases air becomes rarefied. So it exerts less pressure. But when altitude decreases earth gravity pulls the gas molecules towards the ground.
So air becomes dense and it exert high pressure. Humidity means the amount of water vapor present in the atmosphere. Water vapor is lighter than air. If the amount of water vapor is more in a unit volume of air, then atmospheric pressure will be less because moist air contains less oxygen and nitrogen and exerts less pressure. While dry air exerts high pressure as it contains more oxygen and nitrogen.
