FAA Ground School Practice Test

The amount of water vapor that air can hold is primarily influenced by what factor?

1. Altitude

2. Air temperature

3. Humidity level

4. Wind speed

The correct answer is: Air temperature

The correct answer is influenced by air temperature because warmer air can hold significantly more water vapor than cooler air. This relationship is governed by the principles of thermodynamics, specifically the concept that as temperature increases, the kinetic energy of the molecules within the air also increases. This heightened activity allows the air to retain more moisture. As the temperature rises, the saturation point of moisture also rises, meaning that the amount of water vapor needed to reach saturation increases. This is why warm, humid days often feel more uncomfortable than cool, humid days. Factors like altitude, humidity level, and wind speed do play a role in weather and atmospheric conditions, but they do not directly influence the maximum capacity of air to hold water vapor in the same fundamental way that temperature does.