Dry air, by definition, contains no water vapor and thus has a relative humidity of 0%. A parcel of air whose relative humidity is 100% necessarily contains water vapor and is therefore not dry air. read more
Absolute humidity is the mass of water vapor divided by the mass of dry air in a volume of air at a given temperature. The hotter the air is, the more water it can contain. Absolute humidity is expressed as grams of moisture per cubic meter of air (g/m3). read more