Where does moisture come from?
The amount of moisture air can retain is determined by its temperature and, to a lesser extent, its pressure. Any sufficient drop in temperature or increase in pressure will cause moisture to condense out of the air. Relative humidity is the amount of moisture that is present in the air, compared to the total amount the air could hold at a certain temperature. For example: One cubic foot of air at 80°F, 27°C can hold about 12 grains of moisture. If it is holding all 12 grains, it is said to be at 100% relative humidity or saturated. If that same cubic foot of air is holding only 6 grains of moisture, it is at 50% relative humidity. Saturation point is the point at which air is holding all the water vapor it can (100% relative humidity). If we added more water vapor to saturated air, the water vapor would condense into a liquid. Remember that a drop in temperature or increase in pressure will cause moisture to condense out of air that is saturated. Condensation is the changing of water
