Dear Tom,
Why is the moisture content of air reported as a humidity value, expressed as a percentage, and not as the amount of water in a volume of air, such as ounces of water per cubic yard?
---Chuck Gunneson
Dear Chuck,
Relative humidity expressed as a percentage of saturation has been used to express moisture levels for so long that it has become the most familiar measurement for most people. Old habits are hard to break. That said, your point is well taken. You're suggesting that moisture be reported in "absolute" terms, stating exactly how much water would be physically measured if we squeezed all the moisture from the air. Meteorologists do just that; they use a value known as "precipitable water," which expresses the total depth of water in inches in a column of air from the surface upward.
Why is the moisture content of air reported as a humidity value, expressed as a percentage, and not as the amount of water in a volume of air, such as ounces of water per cubic yard?
---Chuck Gunneson
Dear Chuck,
Relative humidity expressed as a percentage of saturation has been used to express moisture levels for so long that it has become the most familiar measurement for most people. Old habits are hard to break. That said, your point is well taken. You're suggesting that moisture be reported in "absolute" terms, stating exactly how much water would be physically measured if we squeezed all the moisture from the air. Meteorologists do just that; they use a value known as "precipitable water," which expresses the total depth of water in inches in a column of air from the surface upward.
