Question

How is Relative Humidity measured and expressed?

Answer 1

Relative Humidity is measured by comparing the actual amount of water vapor present in the air to the maximum amount of water vapor the air can hold at a given temperature. It is expressed as a percentage. This measurement can be done using a hygrometer, often a dry and wet bulb thermometer setup. The wet bulb has a piece of wet cloth wrapped around it, and as water evaporates from this bulb, it cools down relative to the dry bulb. The difference in temperature between the dry and wet bulbs indicates the rate of evaporation and allows the calculation of relative humidity. When both thermometers show the same temperature, it means the air is fully saturated, and the relative humidity is 100%.