Dear Tom,
Could you define “relative humidity” in non-technical terms? I don’t know exactly what it is.
—Allen Pruhaska
Dear Allen,
Popular usage of “humidity” refers to a measure of the atmosphere’s water content or the amount of moisture in the air. What many may not realize is that there are a number of different humidity measure- ments. The reading most widely disseminated to the public is relative humidity. The operative word here is relative. Relative humidity expresses atmospheric moisture as a percentage of the actual amount of water vapor in the air compared to the maximum amount the air can hold at the observed temperature and air pressure. It gives the percentage of saturation (for instance 50% RH means the air is at 50% of saturation. 100% means the air is saturated and can hold no more water in vapor form).