Final answer:
Calm air during the night can lead to less dispersion of vapor and higher moisture concentration, increasing the likelihood of condensation and leading to the formation of dew or fog.
Step-by-step explanation:
During the night, the air tends to be calmer, which causes vapor to disperse less, leading to a higher possibility of condensation. Due to the lack of air currents that would normally help disperse the vapor, the vapor becomes more concentrated and the air can become saturated. When the air temperature falls below the dew point, the excess water vapor condenses into dew or fog. This phenomenon is particularly noticeable under clear skies, where radiation cooling can lead to a significant drop in temperature, increasing the likelihood of reaching the dew point and resulting in condensation.