Introduction | Humidity | Measuring | Dew Point | Calculate | Activity

Dew Point

Why are there water droplets on the grass on a cool summer morning, even though it did not rain the night before? The water most likely came from water vapor condensing from the air when it cooled to the dew point. The dew point is the temperature when water will start to condense out of the air.

The air in Dewdrop’s meter square box below is always at the dew point, saturated as much as possible with vapor. However, air has usually less vapor in it than it actually could. If the temperature is 95 degrees F and the air in Dewdrop’s box has only 0.4 grams of vapor in it, how much would you have to lower the temperature to reach the dew point? To find the answer, take a look at Dewdrop’s box in the pictures below. What is the temperature when air is saturated with 0.4 grams of water? (Answer: 50 degrees F)