Wet-bulb temperature is a measure used to estimate which humidity property?

• A. Relative humidity
• B. Absolute humidity
• C. Vapor pressure
• D. Specific humidity

Answer: (A)

Wet-bulb temperature is a practical way to gauge how close the air is to being fully saturated with moisture, i.e., the relative humidity. The wet-bulb thermometer cools by evaporation: when the air is dry, evaporation happens quickly and the wet-bulb reading drops well below the dry-bulb temperature; when the air is humid, evaporation is slower and the two readings are closer together. By comparing the wet-bulb and dry-bulb readings (often with a psychrometric chart or simple formulas at a given pressure), you can estimate relative humidity. It isn’t a direct measure of absolute humidity, vapor pressure, or specific humidity, which depend on mass or pressure of water vapor rather than how evaporative cooling responds to ambient humidity.