Can Water Vapor Move Through the Air?

Water Particles

• Air is mostly empty space. The particles moving through air mostly do not affect each other, since they do not touch. Therefore, the water vapor particles can move freely throughout the air. Water molecules attract each other, holding themselves together. To evaporate, they must expand to the point where they have less attractive force pulling each other, allowing them to break free from the water body.

Saturation Vapor Pressure

• While people refer to "saturation vapor pressure," this term is a misnomer that came from a time when people thought that water saturated the air. Saturation vapor pressure is actually equilibrium vapor pressure, which results from the amount of heat that energizes the water molecules. Energized water molecules are more likely to leave the body of water and move around more freely. When water evaporates, the molecules eventually flow to where they are less common, causing the air to eventually achieve equilibrium. However, the molecules still flow through the air. In addition, the open atmosphere is too large to achieve equilibrium.

Outer Space

• Water vapor moves throughout outer space. Water vapor is not only on the Earth, but also resides in outer space. It plays an important role in molecular clouds that eventually create stars and planets. Water vapor produces radiation that cools the collapsing cloud material, allowing it to shrink and produce a new star. Water also forms planets by allowing dust grains to clump together. The water then allows molecules to transport so they can facilitate complex chemistry.

Weather

• The largest source of water vapor is the ocean. The sun heats the ocean, causing it to release water vapor into the atmosphere. This strongly controls weather patterns. Clouds come from the movement of water vapor through air. This vapor condenses and the molecules attract to each other, forming the cloud bodies. By understanding the movement of water vapor through the atmosphere, people can predict the weather. For example, swirling water vapor can signal a coming hurricane. Water vapor significantly affects climate by absorbing more thermal energy than any other substance. The amount of water vapor in the air affects the temperature of the Earth.