Water vapor
Introduction
Water vapor, or aqueous vapor, is the gaseous phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Unlike other forms of water, water vapor is invisible. Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation.
Physical Properties
Water vapor differs from most other gases in that it is not a permanent gas. It is a component of the atmosphere, but its concentration varies widely. This is due to the large amounts of water on the Earth's surface and the ability of water to change phase at the temperatures and pressures that occur on the Earth's surface. Water vapor is less dense than most other gases and rises in the atmosphere.
Chemical Properties
Water vapor is a compound of hydrogen and oxygen, with the chemical formula H2O. It is a tasteless, odorless, and colorless gas at room temperature and pressure. Water vapor is a greenhouse gas, and plays a key role in Earth's climate. It absorbs heat from the sun and the Earth's surface, and radiates it back to space.
Role in the Atmosphere
Water vapor plays a crucial role in regulating the Earth's climate. By absorbing and emitting heat, it drives the atmospheric processes that distribute heat around the globe. Water vapor is the most potent greenhouse gas owing to the presence of the hydrogen bond which strongly absorbs in the infrared region of the light spectrum.
Water Vapor and Weather
Water vapor is a key factor in weather. It is the primary source of all precipitation: rain, snow, and other forms of atmospheric condensation. Water vapor is also a key component in the formation of clouds. The amount of water vapor in the atmosphere (humidity) is a major factor in weather patterns and climate zones.
Water Vapor and Climate Change
Water vapor is the most abundant greenhouse gas in the Earth's atmosphere, and it plays a significant role in the Earth's radiative forcing. As a greenhouse gas, it absorbs and emits radiant energy within the thermal infrared range, contributing significantly to global warming.
Measurement and Detection
The amount of water vapor in the atmosphere can be measured using a variety of techniques, including weather balloons, satellites, and ground-based instruments. These measurements are critical for understanding the Earth's climate and predicting weather patterns.