Water vapor can be treated as a gas. At a particular temperature air for example can only hold so much water vapor. The higher the temperature the more water vapor it can hold. When saturated the relative humidity would be 100 % RH, so relative humidity describes how close to saturation the air is. It is important to remember that in a process with a high relative humidity a small drop in temperature will cause the humidity to rise and the environment to saturate. Rapid temperature changes in a an environmental chamber for example could also cause condensation.
Water (H2O) in gaseous form. Also called aqueous vapor . See vapor. The amount of water vapor present in a given gas sample may be expressed in a number of ways. See absolute humidity, mixing ratio, dewpoint, relative humidity, specific humidity, vapor pressure.
Water vapor is the primary gas responsible for the greenhouse effect. It is believed that increases in temperature caused by anthropogenic emissions of greenhouse gases will increase the amount of water vapor in the atmosphere, resulting in additional warming.
Water in gaseous form. It is one of the most import constituents of the atmosphere. Due to its molecular content, air containing water vapor is lighter than dry air. This contributes to the reason why moist air has a tendency to rise.
Water vapor, also aqueous vapor, is the gas phase of water. On the Earth, water vapor is one state of the water cycle within the hydrosphere.Technically called the Hydrologic cycle, from U.S. Geologic Survey. http://ga.water.usgs.gov/edu/watercycle.html Water Cycle.