ACID RAIN

ACID RAIN

The term "acid rain" is commonly used to mean the deposition of acidic components in rain, snow, fog, dew, or dry particles. It can also be referred to as precipitation such as rain or snow which contains a higher level of acid than normal. The more accurate term is "acid precipitation." Distilled water, which contains no carbon dioxide, has a neutral pH of 7. Liquids with a pH less than 7 are acid, and those with a pH greater than 7 are alkaline (or basic). "Clean" or unpolluted rain has a slightly acidic pH of 5.6, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid. Around Washington, D.C., however, the average rain pH is between 4.2 and 4.4.

The extra acidity in rain comes from the reaction of air pollutants, primarily sulfur oxides and nitrogen oxides, with water in the air to form strong acids (like sulfuric and nitric acid). The main sources of these pollutants are vehicles and industrial and power-generating plants. Therefore, acid rain is mainly caused by sulfur dioxide, nitrogen oxide and other pollutants being released into the atmosphere when fossil fuels such as oil or coal containing sulfur are burnt. Carbon combines with sulfur trioxide from sulfur-rich fuel to form particles of an acid substance. The effects of acid rain are primarily felt by wildlife. The water in lakes becomes very clear as fish and microscopic animal life are killed. It is believed that it is acid rain that kills trees, especially conifers, making them gradually lose their leaves and die. Acid rain can damage surfaces such as stone buildings when it falls on them. Acidity in rain is measured by collecting samples of rain and measuring its pH. To find the distribution of rain acidity, weather conditions are monitored and rain samples are collected at sites all over the country.