What is the temperature at which water vapor in the air will start to condense?

• A. Dew point
• B. Relative Humidity
• C. Saturation Point
• D. Freezing Point

Answer: (A)

The dew point is the temperature at which water vapor in the air begins to condense. At this temperature, the air is saturated with moisture, so cooling any further causes vapor to change into liquid water, forming dew, fog, or clouds. The dew point rises with more moisture in the air and falls when the air is drier. Relative humidity describes how close the air is to saturation at the current temperature, but it doesn’t specify the temperature needed for condensation. Saturation point is sometimes used loosely to mean 100% relative humidity, but the precise trigger for condensation is the dew point. The freezing point is about turning water into ice and isn’t what governs condensation.