Acid rain occurs when sulphur dioxide and nitrogen combine with water in the atmosphere to form harmful compounds. These fall on the earth in the form of rain, fog, and snow.

Sulphur dioxide is formed by the burning of fossil fuels such as coal, which contain a high quantity of sulphur. While nitrogen oxides are the by-products of various industrial activities and the exhaust fumes of automobiles.

Acid rain can cause irreparable damage to our environment. The brunt is borne by lakes, forests, crops, and even man-made structures. When acid rain falls in lakes, it can increase the level of acidity. Thus, the lake loses its ability to counteract acidity with alkaline chemicals from the surrounding soils and rocks.

The USA alone emits almost 20 million tonnes of Sulphur Dioxide every year. These three-fourths of Sulphur Dioxide comes from the burning of fossil fuels. Acid rain can travel great distances from the source.  In fact, a 10 to 80 percent increase in acidity has been detected as far away as 4000 km from the source.  Therefore, Half of the acid rain in Canada results from pollution from the USA. India is also susceptible to the threat of acid rain.

Impacts of Acid Rain

Even the Taj Mahal is showing signs of decay on account of acid rain. One of the reasons for the migratory birds in Ghana bird sanctuary disappearing could be the steady acidification of the water body. In a nutshell, acid rain is devastating to live. Thus, there is a need for Measures and control this worldwide.

Species showing the greatest damage are conifers such as fir, pine, and spruce. It is characterized by the yellowing of the needle tips, premature defoliation, and death. Because this occurs high up in the crowns of the trees, few people who stroll through the woods are aware of the damage.

Trees are more susceptible to leaching out of calcium, magnesium, and other nutrients from the soil, which, in turn, is promoted by acidification from acid rain. A pine tree requires the same amount of calcium as wheat does, for growth. In young trees, yellowing of the needle tips is reversed by applying calcium and magnesium compounds at their base. Swedish reports also confirm the deleterious effects of acidic components in the atmosphere. And the damage is not limit to trees.

The tiny sea salt particles have an impact on climate and acid rain. The sea salt absorbs more Sulphur Dioxide and converts it to sulphuric acid. Thus it is a major component of acid rain and contributes to haze in the atmosphere.

The Causes and the Effects

Fish, notably brown trout and salmon, have disappeared from thousands of lakes and several large rivers in Europe, particularly in Scandinavia. The acidity of the atmosphere, which combines with the aluminum present in the soil, is the major factor that causes this damage.

The Mighty Extinction

There has been serious debate over what killed the dinosaurs. There is a suggestion that the acid deposition brought about their extinction. Geologists from the Massachusetts Institute of Technology suggest that a large comet hitting the Earth at 65 km per second would possibly have led to strong acidic rain falling all over the world. The comet weighing 12.5 million billion kilograms would have heated the atmosphere very strongly. As a result, it produces oxides of nitrogen which would have deposited acid of pH less than 1.5 all over the world. This could have killed the dinosaurs.

Other researchers suggest that volcanic eruption over ten thousand years would have produced enough deposition to cause the catastrophe.

Worst Affected Country’s by Acid Rain

Destructive Effect of Acid Rain

Sweden and Canada are the country’s worst impact of acid rain. They assume that the industrial pollutants releases by the neighboring countries are the main causes of acid rain in these countries.

Besides, Gigantic-petrochemical units in North America have caused pollution in Canada, and because of such pollution; acid rain is a frequent occurrence. There is an acceptance that a 15 percent reduction in timber growth in the Scandinavian region is due to acid rain, brought by winds blowing from heavily industrialized Europe. Unchecked acid rain has decayed around 10,000 freshwater lakes in Sweden. This results in the destruction and abnormalities in fish in acidified lakes. Besides, it also results in a substantial reduction in the number of beneficial organisms. Such as bacteria, which sustain life-forms in aquatic habitats.

In Norway, due to acid rain, about 5000 sq. miles of lake land has become barren. Norway and Sweden have dumped thousands of tonnes of lime in their lakes so that the water-bodies can protect themselves from the menace of acid rain. Since more forests are in advanced stages of the disease, the situation is worse still.

Owing to the intensity of acid rain, pine and fir trees in the Netherlands and Switzerland are losing their needles prematurely. Increasing industrialization may cause more damage to the forests in Europe, in the future. According to the World Wildlife Fund, “The effect of acid rain on both forests and freshwater lakes was not simply to eliminate one or two species. It could inhibit fundamental nutrient cycling and cause major losses to vital nutrients, interfere with primary production, disrupt the main biological process and relationship of the ecosystem”.

Project INDOEX

The Indian Ocean Experiment is an international venture. In this venture, it includes scientists from India, the USA, Germany, France, Netherlands, and other European countries.

Dr. Mitra, AP. and his team, the chief scientist, Indian program chair INDOEX has located a huge cloud of pollutants. It is the size of the US that is covering a part of the Indian ocean sky creating fear of acid rain and even low rainfall. The brown haze of pollutants comprises high concentrations of aerosols and other tiny particles and also several gases including carbon monoxide, sulphur dioxide, various organic compounds, etc. The haze covered the northern part of the Indian Ocean, the Arabian Sea, most of the Bay of Bengal, and the equatorial regions of the Indian Ocean. They inferred that the haze has both natural and anthropogenic sources. Experiments conducted by the INDOEX and the BOBMEX (Bay of Bengal Monsoon Experiment) were helped by the National Center for Medium-Range Weather Forecasting (NCMRWF) which now has a new high-end computer system to improve its accuracy and range.


Sulphur and nitrogen oxides released by industrial plants and motor exhausts interact with moisture in the air to form more dangerous sulphuric and nitric acids which fall as acid precipitating far away. Sulphur dioxide is one of the chief culprits of acid rain. It reaches the atmosphere by sea-spray, rotting vegetation, and volcanoes in some places. Burning fuel is oxidized to sulphur trioxide (taking up atoms of oxygen) which dissolves in water, forming sulphuric acid. Fish, notably brown trout and salmon, have extinct from thousands of lakes and several large rivers in Europe due to the acidity of the atmosphere.

In the first phase, acid rain fall-out kills lakes and water bodies. In the second phase, the sulphate combines with soil nutrients and leaches them from the soil. The third phase causes nutrient loss since sulphate, combining with aluminum in the soil, causes toxic aluminum. It also causes a reduction in the number of beneficial organisms, like bacteria, which sustain life-forms in aquatic habitats. There is even an assumption that the extinction of dinosaurs was due to acid rain.

Normal rain is slightly acidic with a pH value of 5.6. In scientific terms, pH is a measure of the acidity and alkaline of solution or a scale ranging from O to 14, 7 being considered neutral.  Concentrations higher than 7 indicate alkalinity and those less than 1 are acidic. The lower the value, the higher the acidity. On a percentage basis, acid rain consists of 65% sulphuric acid, 30% nitric acid, and 5% hydrochloric acid.

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