Why does dry air create more pressure then wet air?

Question

Why does dry air create more pressure then wet air?

Answer 1

Dry is more dense than moist air because water is less dense than dry air. To explain this will involve chemistry. Water = H2O, Oxygen = O and N = Nitrogen. When the air is dry it contains more O & N than H2O. When water vapor increases, than O & N are replaced by more H2O molecules. When this happens the air becomes less dense.

Answer 2

Dry air is actually heavier, or more dense, than "wet" air.  Since water vapor is much less dense than either oxygen or nitrogen, as the amount of water vapor in the air increases, the density of air decreases. At Standard temperature and pressure 22.4 L will weigh

100% O2 = 32 g

100% N2 = 28 g

22% O2 = 7.04 g

78% N2 = 21.84 g

dry air = 21.84 + 7.04 = 28.88 g

21% O2 = 6.72

77% N2 = 21.56

2% H20 = 0.36

wet air = 6.72 + 21.56 + 0.36 = 28.64 g