Normally, rain is slightly acidic. Acid precipitation, however, can have a pH as low as 2.3. The formation of acid deposition in the atmosphere is explained in detail. The process of lake acidification by acidic pollutants is also discussed. Evaporation and transpiration are the two processes that move water from the Earth's surface to its atmosphere.
Evaporation is movement of free water to the atmosphere as a gas.
It requires large amounts of energy. Transpiration is the movement of water through a plant to the atmosphere. Scientists use the term evapotranspiration to describe both processes. The growth of crops is a function of water supply. If crops experience drought, yields are reduced.