The air's capacity to hold water vapor is primarily related to its what?

The air's capacity to hold water vapor is primarily related to its temperature. As temperature increases, the air can hold more moisture because warmer air has greater energy, allowing water molecules to remain in vapor form rather than condensing into liquid. This is why warmer conditions often lead to increased humidity levels.

On the other hand, while humidity is a measure of the amount of water vapor present in the air, it does not determine how much water vapor the air can hold at a given temperature. Altitude can influence temperature and pressure but is not the direct factor that affects the air's capacity for moisture. Pressure can impact the ability of the air to hold water vapor, as warmer air diminishes pressure effects, but the primary relationship is fundamentally tied to temperature.