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Thursday, 29 December 2011

Causes and Effects of Acid Rain

Acid rain is a form of pollution that can cause of lot of damage to natural ecosystems, to man-made objects, as well has harms human health. Here are some of the causes and effects of acid rain.

Acid rain, or more accurately acid precipitation, is the term used for describing rainfall with a pH level lower than 5.6. This type of pollution is a matter of great debate currently due to the potential of its causing environmental damages all across the world. For the last decade or so acid rain has caused destruction to hundreds of lakes and streams in many parts of the world, including the US, Canada, and Europe. Acid rain forms due to the oxides of sulfite and nitrogen combining with the moisture contained in the atmosphere, resulting in the formation of sulfuric and nitric acids. These acids can be dispersed far away from their places of origin.

What are the Causes of Acid Rain?

The oxides of nitrogen, or NOx, and sulfur dioxide, or SO2, are the two main sources of acid rain. Sulfur dioxide, which is a colorless gas, is given off as a by-product when fossil fuels that contain sulfur are burned. This gas is produced due to various industrial processes, like the processing of crude oil, utility factories, and iron and steel factories. Natural means and disaster can also result in sulfur dioxide being released into the atmosphere, such as rotting vegetation, plankton, sea spray, and volcanoes, all of which emit about 10% sulfur dioxide. On the whole, industrial combustion is responsible for 69.4% sulfur dioxide emissions into the atmosphere, and vehicular transportation is responsible for about 3.7%.

Nitrogen oxide is the other chemical that acid rain is made up of. Any nitrogen compound that contains oxygen atoms of any amount is known as oxides of nitrogen. For example, nitrogen dioxide and nitrogen monoxide are oxides of nitrogen. These gases are produced in firing processes which involve extremely high temperatures, e.g., utility plants and automobiles, as well as in chemical industries, such as in the production of fertilizers. Five percent of nitrogen oxide is emitted by natural processes like lightning, volcanic eruptions, forest fires, and action of bacteria in the soil. Industrial processes emit 32% and vehicular transportation is responsible for 43%.

Nitrogen oxide, which is a dangerous gas in itself, causes damage to the respiratory organs by attacking the membranes in them, thus increasing the chances of respiratory diseases. It also causes smog and is a contributory factor for the damage of the ozone layer in the atmosphere. When there is acid rain, the nitrogen oxide can be carried far away from the original location of the rain.

What are the Effects of Acid Rain?

Effects of acid rain on plant life: Acid rain seeps into the earth and poisons plants and trees by dissolving toxic substances in the soil, such as aluminum, which get absorbed by the roots. Acid rain also dissolves the beneficial minerals and nutrients in the soil, which are then washed away before the plants and trees have a chance of using them in order to grow.

When there is frequent acid rain, it corrodes the waxy protective coating of the leaves. When this protective coating on the leaves is lost, it results in making the plant susceptible to disease. When the leaves are damaged, the plant loses its ability to produce sufficient amounts of nutrition for it to stay healthy. Once weakened, the plant becomes vulnerable to the cold weather, insects, and disease, which can lead to its death.

Effects of acid rain on aquatic life: Apart from plants, acid rain also affects aquatic organisms adversely. A high amount of sulfuric acid interferes with the ability of fish to take in nutrients, salt, and oxygen. As far as freshwater fish is concerned, in order for them to stay alive they need to have the ability of maintaining a balance between the minerals and salts in their tissues. The molecules of acid result in mucus forming in their gills, which prevents them from absorbing oxygen in adequate amounts. Plus, the acidity, which reduces the pH level, causes the imbalance of salt in the tissues of fish.

Moreover, this change in the pH level also impairs some of the fish's ability to maintain their calcium levels. This impairs reproduction the ability of the fish, because the eggs become to weak or brittle. Lack of calcium also causes deformed bones and weakened spines.

Effects of acid rain on man-made objects: Apart from causing harm to natural ecosystems, acid rain also damages man-made structures and materials. For example, acid rain dissolves sandstone, limestone, and marble. It also corrodes ceramic, textiles, paints, and metals. Rubber and leather deteriorate if exposed to acid rain. Stone monuments and carvings begin losing their features when exposed to acid rain.

Effects of acid rain on humans: Most of all, acid rain affects human health adversely. It has the ability of harming us via the atmosphere as well as the soil where the food we eat is grown. Acid rain results in toxic metals breaking loose from the chemical compounds they occur in naturally. While toxic metals may be dangerous, but as long as they exist in combination with other elements, they are not harmful. Once acid rain causes these toxic metals to be released they can infiltrate into the drinking water, and the animals or crops that humans use as sources of food. This contaminated food can damage the nerves in children, or result in severe brain damage, or even death. Scientists suspect that aluminum, one of the toxic metals affected by acid rain, is associated with Alzheimer's disease.

Another adverse health effect of acid rain on humans is the respiratory problems it causes. The emissions of nitrogen oxide and sulfur dioxide cause respiratory problems like throat, nose and eye irritation; headache; asthma; and dry coughs. Acid rain is particularly harmful for those who have difficulty in breathing or suffer from asthma. In fact, even the lungs of healthy people can be damaged by the pollutants in acid air. 
(Courtesy: Rita Putatunda)

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