Which of the following factors does NOT affect atmospheric pressure?

Atmospheric pressure is influenced by several factors, among which altitude, temperature, and gravity play significant roles. However, humidity does not directly affect atmospheric pressure in the same manner as the other factors.

Altitude influences pressure because as one ascends in the atmosphere, there is less air above, leading to lower pressure. Temperature affects pressure because warmer air is less dense and tends to rise, which can lead to lower pressure at the surface. Gravity is crucial, as it pulls the air downwards, contributing to the weight of the air column above any point on the Earth's surface and thereby affecting pressure.

While humidity does affect the density of air (moist air is lighter than dry air), it does not change atmospheric pressure on its own. Instead, it can influence the local weather and conditions, but not the fundamental relationship of pressure in the atmosphere as defined by altitude, temperature, and gravity. Therefore, it is accurate to state that humidity does not affect atmospheric pressure in the direct way that the other options do.