Acid rain is a broad term that is often used to describe several forms of acid deposition. Wet deposition is when rain, snow, fog, or mist contains high amounts of sulfuric and nitric acid. When sulfur dioxide and nitrogen oxides are emitted into the atmosphere, they dissolve in water and fall as precipitation. Dry deposition occurs when dust and smoke that contain high amounts of sulphur dioxide and nitrogen oxides settle to the ground, or onto buildings, cars and vegetation. These gases are converted to acids when they contact water. The acidity of acid rain can vary. Pure water has a pH of 7 and normal rainwater has a pH around 5. In , the most acidic rain that fell in the United States had a pH of 4. Acid rain develops when sulfur dioxide or nitrogen oxides enter the atmosphere. While natural processes, such as the eruption of a volcano or decomposing vegetation, can emit sulfur dioxide and nitrogen oxides into the air, acid rain is primarily caused by excessive emissions of sulfur dioxide and nitrogen oxides as a result of human actions.
ACID RAIN FACT SHEET
The fossil fuels that humans burn for energy can come back to haunt us as acid rain.
All rights reserved. Acid rain describes any form of precipitation that contains high levels of nitric and sulfuric acids. It can also occur in the form of snow, fog, and tiny bits of dry material that settle to Earth. Normal rain is slightly acidic, with a pH of 5. Rotting vegetation and erupting volcanoes release some chemicals that can cause acid rain, but most acid rain is a product of human activities. The biggest sources are coal-burning power plants , factories, and automobiles. When humans burn fossil fuels , sulfur dioxide SO 2 and nitrogen oxides NO x are released into the atmosphere. Those air pollutants react with water, oxygen, and other substances to form airborne sulfuric and nitric acid. Winds may spread these acidic compounds through the atmosphere and over hundreds of miles.
What Causes Acid Rain?
Pure water has a pH of 7. As is seen in Table I, carbon dioxide CO 2 is present in the greatest concentration and therefore contributes the most to the natural acidity of rainwater. Carbon dioxide, produced in the decomposition of organic material, is the primary source of acidity in unpolluted rainwater. NOTE: Parts per million ppm is a common concentration measure used in environmental chemistry. The formula for ppm is given by:.
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