Question

When still air cools by radiating at night, it is unusual for temperatures to fall below the dew point. Explain why.

Short answer

At a temperature below the dew point, condensation will take place, and as a result, water vapor in the atmosphere will turn into water.

Step-by-step solution

Define dew point

The dew point is the temperature at which water vapor in the atmosphere condenses to form water. At this temperature, water vapor and water are in equilibrium. So, the rate of condensation will be the same as the rate of evaporation.

Evaporation is the process in which water transforms into water vapor whereas condensation is the process in which water vapor transforms into water.

Explain why the temperature doesn’t fall below the dew point.

At the dew point, the air in the atmosphere is saturated, and it can’t hold the moisture. If the temperature falls below this point, it will condense into water. When still air cools by radiation, dew will be formed, and it will release the latent heat of condensation. This helps to maintain the temperature by not allowing it to fall below the dew point.

So, it is unusual to have a temperature less than the dew point because below this temperature, condensation will take place.