Acid rain is precipitation that contains high levels of nitric or sulfuric acid. Natural and industrial sources can release sulfur dioxide and nitrogen oxide into the atmosphere, leading them to combine chemically with oxygen and water to form their respective acidic molecules. These acids are then deposited through rain or dust depending on the climate of the region. While acid rain can occur anywhere in the world, it is prevalent in regions that have high industrial activity.
The chemicals in acid rain can be introduced into the atmosphere by volcanoes, industrial by-products, fossil-fuel combustion and decaying vegetation. In most industrial countries, electricity generation through fossil fuel combustion releases more than 65 percent of all sulfur dioxide and 25 percent of all nitrogen oxide. Acid rain can potentially cause damage to houses, cars and other materials, as well as natural habitats, such as lakes, streams, wetlands and other aquatic environments.
Why Does it Occur?
Gases released by fossil fuel combustion and volcanic eruptions can rise in to the atmosphere and mix with water and oxygen to form acidic molecules, resulting in sulfuric and nitric acid. This could result in acid rain or dry deposition of acid in dust.
Wet or Dry Deposition
The type of deposition depends on the weather of the region. Wet deposition, or acid rain, occurs when the acidic molecules mix with rain, fog, sleet or snow. As the wet mixture falls, it can harm plants and animals exposed to the acid rain. Dry deposition occurs when the weather is dry and acidic molecules mix with dust or smoke and fall down as dry deposits. Such a mixture can stick to houses, buildings, cars, etc., causing damage in varying degrees. Rain can wash these mixtures, leading to acidic runoff water.
Where Does it Occur?
While acid rain is most prevalent where emissions of sulfur dioxide and nitrogen oxide are high, especially in industrial countries, it can occur anywhere on Earth as winds blow emissions many miles from their sources.