What primarily determines the maximum amount of water vapor that air can hold?

The maximum amount of water vapor that air can hold is primarily determined by air temperature. As the temperature of the air increases, its capacity to hold moisture also increases. This is because warmer air molecules move more energetically, allowing them to accommodate more water vapor in the form of invisible gas.

For example, when the air temperature rises, the saturation point—the maximum amount of moisture that air can hold without condensation—increases. Conversely, cooler air cannot hold as much water vapor, which is why, on cold days, you might notice dew or frost forming.

While relative humidity indicates how much water vapor is in the air compared to how much it can hold at a given temperature, it does not determine the maximum capacity itself. Stability of air and air pressure can influence weather conditions and the behavior of air masses but are not direct factors in determining water vapor capacity. Therefore, air temperature is the foundational element that dictates the saturation point of water vapor in the atmosphere.