The term acid rains are commonly used to mean a deposition of acid components in rain, snow fog, dew or dry particles. That is the rains that are acidified.
This is more accurately called as acid precipitation. Acidic nature is characterized by pH value (acid base equilibrium) of substance. If the substance is have pH value at 7 then that is said to be neutral. If its pH is less that 7 then that is called a acid and if pH is greater than 7 then that is called as base or alkali. If the pH value is close to 0 its strong acid and if pH value is close to 14 it’s a strong base. Anything around 7 is said to be week.
This pH is commonly used as an indicator for the level of acids in the rain. Most commonly it measures around 5.6. This indicates that the rain water that is available is not neutral. It is slightly acidic. This is because carbon dioxide and water in air react with each other to form carbonic acid a weak acid. This acidic nature of the rain will increase with the pollutants. Due to alkaline soil dust in the atmosphere the pH value of the rains some times indicate slightly alkaline nature.
Major pollutants that cause acid deposits are sulfur dioxide and nitrogen oxides which are produced from combustion of fossil fuels. Once these gases are released into atmosphere the get transported into sulfur dioxide and nitric acid and travel long distances before mixing with rain and reaching earth.
This is wet deposition. Some amount will settle on the plants and other surfaces are called as dry deposit. The major sources for the release of these pollutants are from burning fossil fuels. Electricity generation contributes to 70% of the SO2 that is released into the atmosphere which is generated from combustion of coal which contains 2-35 of sulfur in it. Electricity also contributes to 30% of the NOx in the atmosphere. Motor vehicles like buses and trucks contribute around 40% of the NOx from the combustion engines.
Natural calamities such as forests fires, volcanoes contribute around 1-5% of the SO2. forests fires, microbial processes in the soil fuels contribute around 11% of the atmospheric NOx. Industries processing ore containing sulfur to obtain copper, zinc and nickel also release SO2 into atmosphere.
Effects on the society:
The whole world will be affected by the effect of pollution. The destruction caused by these acid rains is not limited to a particular place. Before coming to the earth surface the atmospheric emissions travel for long distances depending the wind and climatic conditions.
Thus the pollution caused at one area will show its effect around that area based on its geographical conditions. It is believed that 50% of the acidic rains in Canada are due to the industrial pollution caused in USA. The side effects of industrialization in England is seen in Norway as acid rains. The problem of acid rains is might have originated from early 1700s where industrial revolution was at its early days and were first discovered in 1872. It gained attention in 1950 and from then the problem have become much worse.
Rural areas around the source are mostly effected as the tall chimneys from the source release the pollutants much higher into the atmosphere and the get carried to rural areas around more easily. Statistics show that half of the black forest is Germany was damaged due to acid rains because of industrial revolution in Germany.
The most severely effected areas due to this acid rains are northeastern parts of US, Southern parts of Canada, Central Europe and Scandinavian parts of Asia specifically India and china, where acid rains are caused by large number of factories and rapid industrialization.
The effect of acid rains are many on the biological and physical geography. Acid rains effects aquatic life, it impacts forests, agricultural sector is effected, the material properties will change. It is believed that acid rains are responsible for dramatic decrease of the acquatic living beings like brook taut and other fish from pristine lakes and streams.
Small organisms can like with excess acid where as big fish cant like in the absence of acid, there by effecting whole marine life. Acid interferes much sooner with reproduction of some species than others. Studies revealed that acid rains are the cause of 70% of the acid contents in lakes and streams. More precise acid rains caused a shit in the fish population from acid-sensitive to acid-tolerant fish and some other aquatic plant and animal species.
Land living animals are also effected by acid rains. The egg size of songbird in Netherlands is seen thinner than to be due to acid rains. The calcium content of the soil and plants is washed into rivers and lakes and into oceans. Snails which depend on the calcium found to be lack them. So songbirds recorded a deficiency of calcium which resulted in the thinner egg size.
Acid rains show impact on the forest echo system also. Acid rains cause depletion of calcium which is vital element for plant growth. Thus the growth of the forest is havocked. In some areas the green leaves turned brown and heavy leaf fall is observed. Acid rains washes away the many useful minerals of the soil that effect plant growth. It causes the release of harmful substances like aluminum into the soil. Acid rains also effect the photosynthesis capabilities if the plants.
Materials and structures are also affected by acid rains. Tajmahal, one of the ten wonders of the world is regularly threatened by acid rains. Famous statues and monuments such as the Lincoln Memorial and Michelangelo’s statue of Marcus Aurelius have started deteriorating because of acid rain. In the year 1952, very thick acid smog killed around 4,000 people.