What happens in the process of evaporation?

Evaporation is the process that changes a liquid into a gas. It can occur at any temperature, and is due to the movement of molecules in the liquid. For example, water left in a saucer will gradually evaporate. The water molecules escape into the air as a gas that is water vapor. The warmer the air, the more moisture it can hold in the form of vapor. Every second, about 15 million tons of moisture is evaporated from the Earth's surface by the heat of the Sun. Water evaporated from the ocean often travels hundreds of miles before falling as rain.

When air contains the maximum water vapor possible for its temperature, it is said to be saturated. Below this temperature, called the dew point for a particular mass of air, the water vapor begins to condense into water droplets.

The amount of water vapor in the air is called its humidity. Relative humidity is the actual amount of water vapor in the air compared with the amount the air would hold if saturated. Relative humidity is usually expressed as a percentage, and in many regions is of major importance in weather reports. Humidity is very high in the tropics, particularly in coastal regions.