 Water vapor is the gas phase of water. Water vapor is just one stage in the water cycle, within the hydrosphere. It can be produced through the boiling or evaporation of water in it's liquid form, also through the sublimation of water in it's ice form. With normal conditions in the atmosphere, water vapor is constantly created by evaporation and expunged by condensation.  Humidity is the amount of water vapor in the air. A device used to measure humidity is called psychrometer or hygrometer. Hygrometers are used to measure relative humidity. Most modern devices utilize temperature of condensation, changes in electrical resistance, and changes in electrical capacitance to measure changes in humidity. Dew forms when water condenses into droplets. When surface temperature falls, ultimately reaching the dew point, water vapor in the atmosphere thickens to form small droplets on the surface. For frost to form the deposition surface has to be colder than the air surrounding it. |
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