The ratio of the actual vapor pressure to the saturated vapor pressure at a given temperature defines what?

• A. Relative humidity
• B. Dew point
• C. Vapor pressure deficit
• D. Specific humidity

Answer: (D)

The ratio of the actual vapor pressure to the saturated vapor pressure at a given temperature is relative humidity. It measures how much moisture the air actually contains compared to how much it could hold at that temperature. If you divide the actual vapor pressure by the saturation vapor pressure and multiply by 100, you get the relative humidity percentage. When the air is holding all it can at that temperature, the ratio is 1 (or 100%).

Dew point is the temperature at which air must be cooled to become saturated and condense water. Vapor pressure deficit is the difference between the actual vapor pressure and the saturation vapor pressure, indicating how much more moisture the air can hold. Specific humidity is the mass of water vapor per mass of dry air, a moisture content term not expressed as a ratio to saturation.