acid precipitation

views updated

acid precipitation Precipitation that has a pH lower than about 5.0, which is the value produced when naturally occurring carbon dioxide, sulphate, and nitrogen oxides dissolve into water droplets in clouds. The increased acidity may be caused naturally (e.g. by gases and aerosols ejected by a volcanic eruption) or by anthropogenic emissions (e.g. from the burning of fuel). The effects of acid precipitation on vegetation, soils, and surface waters are complex, their severity depending on the form of deposition (e.g. acid rain washes rapidly from plant surfaces, but may affect soil; acid mist tends to coat leaves, making it more harmful than rain), and the pH and natural buffering of the soil and water into which it falls. See buffer.