The amount of water vapor air can hold depends on what parameter?

• A. Air temperature
• B. Humidity
• C. Pressure
• D. Wind speed

Answer: (A)

The amount of water vapor air can hold is determined by temperature because the saturation vapor pressure—the maximum moisture air can contain before it becomes saturated—increases as temperature rises. Warmer air has more kinetic energy, allowing more water molecules to stay in the vapor phase, so the capacity to hold water vapor goes up with temperature. Humidity describes how much moisture is currently present relative to that maximum, so it tells you how close you are to saturation but not the capacity itself. Pressure and wind speed influence other aspects of moisture behavior, but they don’t set the air’s maximum moisture-holding capacity the way temperature does. At higher temperatures the air can hold more water vapor; as it cools, capacity drops and condensation can occur.