When the dew point is below 0°C, which of the following occurs?

• A. Water vapor condenses directly into ice, forming frost.
• B. No condensation occurs because the air is too cold.
• C. Water vapor evaporates more rapidly.
• D. Water vapor condenses into liquid water, forming dew.

Answer: (A)

Verified step by step guidance

1. Understand the concept of dew point: The dew point is the temperature at which air becomes saturated with water vapor and condensation begins.
2. Recognize that when the dew point is below 0°C, the temperature at which condensation occurs is below the freezing point of water.
3. Recall that if condensation happens below 0°C, water vapor does not form liquid water but instead changes directly from gas to solid, a process called deposition.
4. Identify that this deposition of water vapor directly into ice crystals on surfaces is what forms frost.
5. Conclude that when the dew point is below 0°C, water vapor condenses directly into ice, forming frost, rather than liquid dew.