Which term describes the ratio of actual water vapor in the air to the amount of water vapor the air would hold if saturated at the same temperature and pressure?

Which term describes the ratio of actual water vapor in the air to the amount of water vapor the air would hold if saturated at the same temperature and pressure?

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

Answer: (B)

The main idea is how full the air is of moisture relative to how much it could hold at the current temperature and pressure. This is expressed as relative humidity—the current amount of water vapor divided by the maximum amount the air could hold at that temperature and pressure, shown as a percentage. Temperature changes the air’s capacity to hold moisture, so relative humidity can vary even if the actual moisture stays the same. Humidity ratio, on the other hand, is the mass of water vapor per mass of dry air, not a comparison to saturation. Dew point is the temperature at which air becomes saturated and condensation begins, and vapor pressure deficit is the gap between saturation vapor pressure and actual vapor pressure.

The main idea is how full the air is of moisture relative to how much it could hold at the current temperature and pressure. This is expressed as relative humidity—the current amount of water vapor divided by the maximum amount the air could hold at that temperature and pressure, shown as a percentage. Temperature changes the air’s capacity to hold moisture, so relative humidity can vary even if the actual moisture stays the same. Humidity ratio, on the other hand, is the mass of water vapor per mass of dry air, not a comparison to saturation. Dew point is the temperature at which air becomes saturated and condensation begins, and vapor pressure deficit is the gap between saturation vapor pressure and actual vapor pressure.