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As temperature decreases, how do dew point and relative humidity change?

  • A

    Dew point remains constant, relative humidity decreases.

  • B

    Dew point remains constant, relative humidity increases.

  • C

    Dew point decreases, relative humidity increases.

  • D

    Dew point increases, relative humidity decreases.

Refer to figure.
Relative Humidity is determined by both moisture content and temperature. It is expressed as a percentage and indicates how close the air is to saturation. For instance, if the relative humidity is 100%, the air is fully saturated with water vapor. If it is 50%, the air contains half the amount of water vapor needed for saturation. The relative humidity also varies with air temperature:

  • As temperature rises, air can hold more water molecules. Therefore, if the amount of water vapor remains constant and the temperature increases, the relative humidity decreases.
  • Conversely, colder air requires less moisture to reach saturation compared to warmer air, so a drop in temperature increases relative humidity.

The dew point is the temperature at which air becomes saturated with moisture. Dry air has a low dew point, meaning it must be significantly cooled to reach saturation. Conversely, humid air has a high dew point relative to its temperature, indicating a smaller temperature-dew point spread.

Dew point is a more reliable indicator of humidity than relative humidity because dew point is not affected by a change in air temperature and doesn’t fluctuate much throughout the day.

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