Which statement about relative humidity and the dew point is most accurate?

Which statement about relative humidity and the dew point is most accurate?

• A. Relative humidity is the current amount of water vapour in the air relative to saturation at that temperature; the dew point is the temperature at which air becomes saturated.
• B. Relative humidity is the air pressure; the dew point is the ambient temperature.
• C. Relative humidity measures wind speed; the dew point relates to cloud type.
• D. Relative humidity is the dew point; the dew point is humidity.

Answer: (A)

Relative humidity indicates how much water vapor is present in the air compared with the maximum amount the air can hold at the current temperature. The dew point is the temperature to which air must be cooled (at the current pressure) for it to become saturated and for condensation to begin. That combination is the clearest way to describe how moisture in the air behaves: RH is a percentage of saturation at the present temperature, while the dew point marks the temperature at which saturation would occur. For example, at 25°C with 60% RH, cooling the air to about the dew point (often around 15°C, depending on pressure) would bring condensation. The other statements mix up concepts—relative humidity isn’t air pressure or wind speed, and the dew point isn’t simply the ambient temperature.

Relative humidity indicates how much water vapor is present in the air compared with the maximum amount the air can hold at the current temperature. The dew point is the temperature to which air must be cooled (at the current pressure) for it to become saturated and for condensation to begin. That combination is the clearest way to describe how moisture in the air behaves: RH is a percentage of saturation at the present temperature, while the dew point marks the temperature at which saturation would occur. For example, at 25°C with 60% RH, cooling the air to about the dew point (often around 15°C, depending on pressure) would bring condensation. The other statements mix up concepts—relative humidity isn’t air pressure or wind speed, and the dew point isn’t simply the ambient temperature.