What is meant by the absolute humidity of the atmosphere?

• A. The actual amount of water that is in a given volume of air.
• B. The total possible water capacity at a given temperature.
• C. The humidity ratio of air at standard conditions.
• D. The share of water vapor in the air relative to dry air.

Answer: (A)

Absolute humidity is the actual amount of water vapor in a given volume of air, usually expressed as grams of water per cubic meter. It reflects the true moisture content at that moment and depends on temperature and pressure because warmer air expands, spreading the same amount of water vapor over a larger volume (lower grams per cubic meter), while cooler air compresses it into a smaller volume (higher grams per cubic meter). This distinguishes it from saturation, which is the maximum amount of water air can hold at a given temperature; from the humidity ratio, which is the mass of water vapor per mass of dry air; and from a simple share relative to dry air, which isn’t the direct measure of moisture per volume.