American Meteorological Society Certification (AMS) Practice

What phenomenon occurs when air reaches the dew point?

1. Air becomes warmer

2. Condensation begins to happen

3. Evaporation increases

4. The humidity level decreases

The correct answer is: Condensation begins to happen

When air reaches the dew point, it cools to the temperature at which it becomes saturated with moisture, leading to the beginning of condensation. This phenomenon happens because the capacity of air to hold water vapor diminishes as it cools. When the air temperature drops to the dew point, the water vapor in the air begins to condense into tiny droplets, forming clouds, fog, or dew, depending on the surrounding conditions. This process is a critical component of the water cycle and weather formation. Other options do not accurately reflect what occurs at the dew point. For instance, air does not become warmer at the dew point; in fact, cooling is necessary for condensation to occur. Additionally, evaporation decreases as humidity levels rise since the air is already close to saturation, and the humidity level does not decrease when the dew point is reached.